diff --git a/common/src/module/canvas.mjs b/common/src/module/canvas.mjs
index 913442f..ba6d5ca 100644
--- a/common/src/module/canvas.mjs
+++ b/common/src/module/canvas.mjs
@@ -530,14 +530,14 @@ class CanvasAPI extends Module {
                     if(this.#redrawCount === currentRedrawCount)
                         callback(imgData)
                     else
-                        console.log("1Discard render of", imgData.source, this.#redrawCount, currentRedrawCount)
+                        console.log("1. Discard render of", imgData.source, this.#redrawCount, currentRedrawCount)
                 })
             } else {
                 // Callback directly
                 if(this.#redrawCount === currentRedrawCount)
                     callback(imgData)
                 else
-                    console.log("2Discard render of", imgData.source, this.#redrawCount, currentRedrawCount)
+                    console.log("2. Discard render of", imgData.source, this.#redrawCount, currentRedrawCount)
             }
         }
         const prerendered = Latex.findPrerendered(ltxText, this.textsize, color)
diff --git a/common/test/mock/latex.mjs b/common/test/mock/latex.mjs
index ab56999..c0a029c 100644
--- a/common/test/mock/latex.mjs
+++ b/common/test/mock/latex.mjs
@@ -23,6 +23,10 @@ const PIXEL = "iVBORw0KGgoAAAANSUhEUgAAAAEAAAABAQAAAAA3bvkkAAAACklEQVR4AWNgAAAAA
 export class MockLatex {
     constructor() {
     }
+    
+    get supportsAsyncRender() {
+        return true
+    }
 
     /**
      * Creates a simple string hash.
@@ -55,13 +59,23 @@ export class MockLatex {
         return `${TMP}/${name}.png`
     }
 
+    /**
+     * @param {string} markup - LaTeX markup to render
+     * @param {number} fontSize - Font size (in pt) to render
+     * @param {string} color - Color of the text to render
+     * @returns {Promise<string>} - Comma separated data of the image (source, width, height)
+     */
+    async renderAsync(markup, fontSize, color) {
+        return this.renderSync(markup, fontSize, color)
+    }
+
     /**
      * @param {string} markup - LaTeX markup to render
      * @param {number} fontSize - Font size (in pt) to render
      * @param {string} color - Color of the text to render
      * @returns {string} - Comma separated data of the image (source, width, height)
      */
-    render(markup, fontSize, color) {
+    renderSync(markup, fontSize, color) {
         const file = this.__getFileName(markup, fontSize, color)
         writeFileSync(file, PIXEL, "base64")
         return `${file},1,1`
@@ -87,4 +101,4 @@ export class MockLatex {
     checkLatexInstallation() {
         return true // We're not *actually* doing any latex.
     }
-}
\ No newline at end of file
+}
diff --git a/runtime-pyside6/LogarithmPlotter/util/js.py b/runtime-pyside6/LogarithmPlotter/util/js.py
index 05f30d5..944c2b0 100644
--- a/runtime-pyside6/LogarithmPlotter/util/js.py
+++ b/runtime-pyside6/LogarithmPlotter/util/js.py
@@ -75,6 +75,7 @@ class PyJSValue:
         return value
 
     def type(self) -> any:
+        ret = None
         matcher = [
             (lambda: self.qjs_value.isArray(), list),
             (lambda: self.qjs_value.isBool(), bool),
@@ -93,8 +94,9 @@ class PyJSValue:
         ]
         for (test, value) in matcher:
             if test():
-                return value
-        return None
+                ret = value
+                break
+        return ret
 
     def primitive(self):
         """
diff --git a/runtime-pyside6/LogarithmPlotter/util/promise.py b/runtime-pyside6/LogarithmPlotter/util/promise.py
index e475b36..f43e85b 100644
--- a/runtime-pyside6/LogarithmPlotter/util/promise.py
+++ b/runtime-pyside6/LogarithmPlotter/util/promise.py
@@ -31,7 +31,7 @@ def check_callable(function: Callable|QJSValue) -> Callable|None:
     """
     if isinstance(function, QJSValue) and function.isCallable():
         return PyJSValue(function)
-    elif isinstance(function, Callable):
+    elif callable(function):
         return function
     return None
 
@@ -51,9 +51,7 @@ class PyPromiseRunner(QRunnable):
     def run(self):
         try:
             data = self.runner(*self.args)
-            if isinstance(data, QObject):
-                data = data
-            elif type(data) in [int, str, float, bool, bytes]:
+            if type(data) in [int, str, float, bool]:
                 data = QJSValue(data)
             elif data is None:
                 data = QJSValue.SpecialValue.UndefinedValue
@@ -62,7 +60,7 @@ class PyPromiseRunner(QRunnable):
             elif isinstance(data, PyJSValue):
                 data = data.qjs_value
             else:
-                raise InvalidReturnValue("Must return either a primitive, a valid QObject, JS Value, or None.")
+                raise InvalidReturnValue("Must return either a primitive, a JS Value, or None.")
             self.promise.fulfilled.emit(data)
         except Exception as e:
             try:
@@ -75,11 +73,11 @@ class PyPromiseRunner(QRunnable):
 
 class PyPromise(QObject):
     """
-    Asynchronous Promise-like object meant to interface between Python and Javascript easily.
+    Threaded A+/Promise implementation meant to interface between Python and Javascript easily.
     Runs to_run in another thread, and calls fulfilled (populated by then) with its return value.
     """
-    fulfilled = Signal((QJSValue,), (QObject,))
-    rejected = Signal(Exception)
+    fulfilled = Signal(QJSValue)
+    rejected = Signal(str)
 
     def __init__(self, to_run: Callable|QJSValue, args=[], start_automatically=True):
         QObject.__init__(self)
@@ -94,7 +92,7 @@ class PyPromise(QObject):
             raise ValueError("New PyPromise created with invalid function")
         self._runner = PyPromiseRunner(to_run, self, args)
         if start_automatically:
-            self._start()
+            self.start()
     
     @Slot()
     def start(self, *args, **kwargs):
@@ -117,31 +115,60 @@ class PyPromise(QObject):
         """
         on_fulfill = check_callable(on_fulfill)
         on_reject = check_callable(on_reject)
-        if on_fulfill is not None:
-            self._fulfills.append(on_fulfill)
-        if on_reject is not None:
-            self._rejects.append(on_reject)
+        self._fulfills.append(on_fulfill)
+        self._rejects.append(on_reject)
         return self
+    
+    def calls_upon_fulfillment(self, function: Callable | QJSValue) -> bool:
+        """
+        Returns True if the given function will be callback upon the promise fulfillment.
+        False otherwise.
+        """
+        return self._calls_in(function, self._fulfills)
+    
+    def calls_upon_rejection(self, function: Callable | QJSValue) -> bool:
+        """
+        Returns True if the given function will be callback upon the promise rejection.
+        False otherwise.
+        """
+        return self._calls_in(function, self._rejects)
+        
+    def _calls_in(self, function: Callable | QJSValue, within: list) -> bool:
+        """
+        Returns True if the given function resides in the given within list, False otherwise.
+        Internal method of calls_upon_fulfill
+        """
+        function = check_callable(function)
+        ret = False
+        if isinstance(function, PyJSValue):
+            found = next((f for f in within if f.qjs_value == function.qjs_value), None)
+            ret = found is not None
+        elif callable(function):
+            found = next((f for f in within if f == function), None)
+            ret = found is not None
+        return ret
 
     @Slot(QJSValue)
     @Slot(QObject)
     def _fulfill(self, data):
         self._state = "fulfilled"
         no_return = [None, QJSValue.SpecialValue.UndefinedValue]
-        for on_fulfill in self._fulfills:
+        print("Fulfill")
+        for i in range(len(self._fulfills)):
             try:
-                result = on_fulfill(data)
+                result = self._fulfills[i](data)
                 result = result.qjs_value if isinstance(result, PyJSValue) else result
                 data = result if result not in no_return else data  # Forward data.
             except Exception as e:
-                self._reject(repr(e))
+                self._reject(repr(e), start_at=i)
                 break
 
     @Slot(QJSValue)
     @Slot(str)
-    def _reject(self, error):
+    def _reject(self, error, start_at=0):
         self._state = "rejected"
         no_return = [None, QJSValue.SpecialValue.UndefinedValue]
-        for on_reject in self._rejects:
-            result = on_reject(error)
+        for i in range(start_at, len(self._rejects)):
+            result = self._rejects[i](error)
+            result = result.qjs_value if isinstance(result, PyJSValue) else result
             error = result if result not in no_return else error  # Forward data.
diff --git a/runtime-pyside6/tests/__init__.py b/runtime-pyside6/tests/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/runtime-pyside6/tests/plugins/__init__.py b/runtime-pyside6/tests/plugins/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/runtime-pyside6/tests/plugins/natural/__init__.py b/runtime-pyside6/tests/plugins/natural/__init__.py
new file mode 100644
index 0000000..4cfe179
--- /dev/null
+++ b/runtime-pyside6/tests/plugins/natural/__init__.py
@@ -0,0 +1,22 @@
+"""
+ *  LogarithmPlotter - 2D plotter software to make BODE plots, sequences and distribution functions.
+ *  Copyright (C) 2021-2024  Ad5001
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program.  If not, see <https://www.gnu.org/licenses/>.
+"""
+
+from .spy import Spy
+from .that import that
+from .interfaces.base import Assertion
+
diff --git a/runtime-pyside6/tests/plugins/natural/interfaces/__init__.py b/runtime-pyside6/tests/plugins/natural/interfaces/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/runtime-pyside6/tests/plugins/natural/interfaces/assertion.py b/runtime-pyside6/tests/plugins/natural/interfaces/assertion.py
new file mode 100644
index 0000000..e1e43c4
--- /dev/null
+++ b/runtime-pyside6/tests/plugins/natural/interfaces/assertion.py
@@ -0,0 +1,39 @@
+"""
+ *  LogarithmPlotter - 2D plotter software to make BODE plots, sequences and distribution functions.
+ *  Copyright (C) 2021-2024  Ad5001
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program.  If not, see <https://www.gnu.org/licenses/>.
+"""
+
+class Assertion(Exception):
+    def __init__(self, assertion: bool, message: str, invert: bool):
+        self.assertion = assertion
+        self.message = message
+        self.invert = invert
+
+    def _invert_message(self):
+        for verb in ('is', 'was', 'has', 'have'):
+            for negative in ("n't", ' not', ' never', ' no'):
+                self.message = self.message.replace(f"{verb}{negative}", verb.upper())
+
+    def __str__(self):
+        return self.message
+
+    def __bool__(self):
+        if not self.invert and not self.assertion:
+            raise self
+        if self.invert and self.assertion:
+            self._invert_message()
+            raise self
+        return True # Raises otherwise.
\ No newline at end of file
diff --git a/runtime-pyside6/tests/plugins/natural/interfaces/base.py b/runtime-pyside6/tests/plugins/natural/interfaces/base.py
new file mode 100644
index 0000000..0786285
--- /dev/null
+++ b/runtime-pyside6/tests/plugins/natural/interfaces/base.py
@@ -0,0 +1,171 @@
+"""
+ *  LogarithmPlotter - 2D plotter software to make BODE plots, sequences and distribution functions.
+ *  Copyright (C) 2021-2024  Ad5001
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program.  If not, see <https://www.gnu.org/licenses/>.
+"""
+from typing import Self, Callable, Any
+
+from .assertion import Assertion
+from .utils import repr_
+
+
+class AssertionInterface:
+    """
+    Most basic assertion interface.
+    You probably want to use BaseAssertionInterface
+    """
+
+    def __init__(self, value, parent: Self = None):
+        self._value = value
+        self._parent = parent
+        if parent is None:
+            self.__not = False
+
+    @property
+    def _not(self) -> bool:
+        """
+        Internal state of whether the expression was negated.
+        Use "not_" to set it.
+        :return:
+        """
+        return self.__not if self._parent is None else self._parent._not
+
+    @_not.setter
+    def _not(self, value: bool):
+        if self._not is True:
+            raise RuntimeError("Cannot call is_not or was_not twice in the same statement.")
+        if self._parent is None:
+            self.__not = True
+        else:
+            self._parent._not = True
+
+    def instance_of(self, type_: type) -> Assertion:
+        """
+        Checks if the current value is equal to the provided value
+        """
+        value_type_name = type(self._value).__name__
+        if not isinstance(type_, type):
+            raise RuntimeError("Provided 'type' provided is not a class.")
+        return Assertion(
+            isinstance(self._value, type_),
+            f"The value ({value_type_name} {repr_(self._value)}) is not a {type_.__name__}.",
+            self._not
+        )
+
+    def __call__(self, condition: Callable[[Any], bool]) -> Assertion:
+        """
+        Apply condition to value that returns whether or not the value is valid.
+        """
+        return Assertion(
+            condition(self._value),
+            f"The value ({repr_(self._value)}) did not match given conditions.",
+            self._not
+        )
+
+    """
+    NOT Properties.
+    """
+
+    @property
+    def NOT(self) -> Self:
+        self._not = True
+        return self
+
+    @property
+    def not_(self) -> Self:
+        self._not = True
+        return self
+
+    @property
+    def never(self) -> Self:
+        self._not = True
+        return self
+
+    """
+    Chain self properties to sound natural
+    """
+
+    @property
+    def that(self) -> Self:
+        return self
+
+    @property
+    def is_(self) -> Self:
+        return self
+
+    @property
+    def does(self) -> Self:
+        return self
+
+    @property
+    def was(self) -> Self:
+        return self
+
+    @property
+    def been(self) -> Self:
+        return self
+
+    @property
+    def have(self) -> Self:
+        return self
+
+    @property
+    def has(self) -> Self:
+        return self
+
+    @property
+    def a(self) -> Self:
+        return self
+
+    @property
+    def an(self) -> Self:
+        return self
+
+
+class EqualAssertionInterface(AssertionInterface):
+    """
+    Interface created for when its value should be checked for equality
+    """
+
+    def __init__(self, value, parent: AssertionInterface = None):
+        super().__init__(value, parent)
+
+    def __call__(self, value) -> Assertion:
+        return Assertion(
+            value == self._value,
+            f"The value {repr_(self._value)} is different from {repr(value)}.",
+            self._not
+        )
+
+    @property
+    def to(self) -> Self:
+        return self
+
+
+class BaseAssertionInterface(AssertionInterface):
+
+    @property
+    def equals(self) -> EqualAssertionInterface:
+        """
+        Checks if the current value is equal to the provided value
+        """
+        return EqualAssertionInterface(self._value, self)
+
+    @property
+    def equal(self) -> EqualAssertionInterface:
+        """
+        Checks if the current value is equal to the provided value
+        """
+        return self.equals
diff --git a/runtime-pyside6/tests/plugins/natural/interfaces/basic.py b/runtime-pyside6/tests/plugins/natural/interfaces/basic.py
new file mode 100644
index 0000000..25d45cb
--- /dev/null
+++ b/runtime-pyside6/tests/plugins/natural/interfaces/basic.py
@@ -0,0 +1,83 @@
+"""
+ *  LogarithmPlotter - 2D plotter software to make BODE plots, sequences and distribution functions.
+ *  Copyright (C) 2021-2024  Ad5001
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program.  If not, see <https://www.gnu.org/licenses/>.
+"""
+from .assertion import Assertion
+from .base import BaseAssertionInterface
+from .int import NumberInterface
+from .utils import repr_
+
+
+class FixedIteratorInterface(BaseAssertionInterface):
+    @property
+    def length(self) -> NumberInterface:
+        return NumberInterface(len(self._value), self)
+
+    def elements(self, *elements) -> Assertion:
+        tests = [repr_(elem) for elem in elements if elem not in self._value]
+        return Assertion(
+            len(tests) == 0,
+            f"This value ({repr_(self._value)}) does not have elements {', '.join(tests)}.",
+            self._not
+        )
+
+    def element(self, element) -> Assertion:
+        return Assertion(
+            element in self._value,
+            f"This value ({repr_(self._value)}) does not have element {repr_(element)}.",
+            self._not
+        )
+
+    def contains(self, *elements) -> Assertion:
+        """
+        Check if the element(s) are contained in the iterator.
+        """
+        if len(elements) == 1:
+            return self.element(elements[0])
+        else:
+            return self.elements(*elements)
+
+    def contain(self, *elements):
+        """
+        Check if the element(s) are contained in the iterator.
+        """
+        return self.contains(*elements)
+
+
+class BoolInterface(BaseAssertionInterface):
+    @property
+    def true(self):
+        return Assertion(
+            self._value == True,
+            f"The value ({repr_(self._value)}) is not True.",
+            self._not
+        )
+
+    @property
+    def false(self):
+        return Assertion(
+            self._value == False,
+            f"The value ({repr_(self._value)}) is not False.",
+            self._not
+        )
+
+
+class StringInterface(FixedIteratorInterface):
+    pass
+
+
+class ListInterface(FixedIteratorInterface):
+    pass
diff --git a/runtime-pyside6/tests/plugins/natural/interfaces/int.py b/runtime-pyside6/tests/plugins/natural/interfaces/int.py
new file mode 100644
index 0000000..7ac8871
--- /dev/null
+++ b/runtime-pyside6/tests/plugins/natural/interfaces/int.py
@@ -0,0 +1,321 @@
+"""
+ *  LogarithmPlotter - 2D plotter software to make BODE plots, sequences and distribution functions.
+ *  Copyright (C) 2021-2024  Ad5001
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program.  If not, see <https://www.gnu.org/licenses/>.
+"""
+from idlelib.configdialog import is_int
+from math import log10, floor, ceil
+from typing import Self
+
+from .assertion import Assertion
+from .base import AssertionInterface
+from .utils import repr_
+
+
+class NumberComparisonAssertionInterface(AssertionInterface):
+    def __init__(self, value, parent: AssertionInterface = None):
+        super().__init__(value, parent)
+        self._compare_stack = []
+
+    def _generate_compare_to(self) -> int:
+        """
+        The number generated by the comparison stack.
+        E.g. can parse one.hundred.million.and.thirty.three.thousand.and.twelve.hundred.and.seven
+                    as ['one', 'hundred', 'million', 'thirty', 'three', 'thousand', 'twelve', 'hundred', 'seven']
+         which results 100,034,207
+        """
+        minus = len(self._compare_stack) > 0 and self._compare_stack[0] == -1
+        if len(self._compare_stack) < (2 if minus else 1):
+            raise RuntimeError("No number to compare the value to provided.")
+        if minus:
+            self._compare_stack.pop(0)
+        # Compute the number
+        add_stack = [self._compare_stack.pop(0)]
+        for element in self._compare_stack:
+            last_power = floor(log10(abs(add_stack[-1])))
+            current_power = floor(log10(abs(element)))
+            if last_power < current_power:  # E.g. one hundred
+                add_stack[-1] *= element
+            elif last_power == 1 and current_power == 0:  # E.g thirty four
+                add_stack[-1] += element
+            elif last_power > current_power:  # E.g a hundred and five
+                add_stack.append(element)
+            else:
+                raise RuntimeError(f"Cannot chain two numbers with the same power ({add_stack[-1]} => {element}.")
+        total = sum(add_stack)
+        return -total if minus else total
+
+    def _compare(self) -> Assertion:
+        raise RuntimeError(f"No comparison method defined in {type(self).__name__}.")
+
+    def __bool__(self) -> bool:
+        return bool(self._compare())
+
+    def __call__(self, compare_to: int) -> Self:
+        if type(compare_to) not in (float, int):
+            raise RuntimeError(f"Cannot compare number ({self._value}) to non number ({repr_(compare_to)}).")
+        self._compare_stack.append(compare_to)
+        return self
+
+    """
+    Chain self properties
+    """
+
+    @property
+    def and_(self) -> Self:
+        return self
+
+    @property
+    def AND(self) -> Self:
+        return self
+
+    """
+    Number shorthands
+    """
+
+    @property
+    def once(self) -> Self:
+        return self(1)
+
+    @property
+    def twice(self) -> Self:
+        return self(2)
+
+    @property
+    def thrice(self) -> Self:
+        return self(3)
+
+    @property
+    def minus(self) -> Self:
+        return self(-1)
+
+    @property
+    def zero(self) -> Self:
+        return self(0)
+
+    @property
+    def one(self) -> Self:
+        return self(1)
+
+    @property
+    def two(self) -> Self:
+        return self(2)
+
+    @property
+    def three(self) -> Self:
+        return self(3)
+
+    @property
+    def four(self) -> Self:
+        return self(4)
+
+    @property
+    def five(self) -> Self:
+        return self(5)
+
+    @property
+    def six(self) -> Self:
+        return self(6)
+
+    @property
+    def seven(self) -> Self:
+        return self(7)
+
+    @property
+    def eight(self) -> Self:
+        return self(8)
+
+    @property
+    def nine(self) -> Self:
+        return self(9)
+
+    @property
+    def ten(self) -> Self:
+        return self(10)
+
+    @property
+    def eleven(self) -> Self:
+        return self(11)
+
+    @property
+    def twelve(self) -> Self:
+        return self(12)
+
+    @property
+    def thirteen(self) -> Self:
+        return self(13)
+
+    @property
+    def fourteen(self) -> Self:
+        return self(14)
+
+    @property
+    def fifteen(self) -> Self:
+        return self(15)
+
+    @property
+    def sixteen(self) -> Self:
+        return self(16)
+
+    @property
+    def seventeen(self) -> Self:
+        return self(17)
+
+    @property
+    def eighteen(self) -> Self:
+        return self(18)
+
+    @property
+    def nineteen(self) -> Self:
+        return self(19)
+
+    @property
+    def twenty(self) -> Self:
+        return self(20)
+
+    @property
+    def thirty(self) -> Self:
+        return self(30)
+
+    @property
+    def forty(self) -> Self:
+        return self(40)
+
+    @property
+    def fifty(self) -> Self:
+        return self(50)
+
+    @property
+    def sixty(self) -> Self:
+        return self(60)
+
+    @property
+    def seventy(self) -> Self:
+        return self(70)
+
+    @property
+    def eighty(self) -> Self:
+        return self(80)
+
+    @property
+    def ninety(self) -> Self:
+        return self(90)
+
+    @property
+    def hundred(self) -> Self:
+        return self(100)
+
+    @property
+    def thousand(self) -> Self:
+        return self(1_000)
+
+    @property
+    def million(self) -> Self:
+        return self(1_000_000)
+
+    @property
+    def billion(self) -> Self:
+        return self(1_000_000_000)
+
+
+class LessThanComparisonInterface(NumberComparisonAssertionInterface):
+    def _compare(self) -> Assertion:
+        compare = self._generate_compare_to()
+        return Assertion(
+            self._value < compare,
+            f"The value ({repr_(self._value)}) is not less than to {repr_(compare)}.",
+            self._not
+        )
+
+
+class MoreThanComparisonInterface(NumberComparisonAssertionInterface):
+    def _compare(self) -> Assertion:
+        compare = self._generate_compare_to()
+        return Assertion(
+            self._value > compare,
+            f"The value ({repr_(self._value)}) is not more than to {repr_(compare)}.",
+            self._not
+        )
+
+
+class AtLeastComparisonInterface(NumberComparisonAssertionInterface):
+    def _compare(self) -> Assertion:
+        compare = self._generate_compare_to()
+        return Assertion(
+            self._value >= compare,
+            f"The value ({repr_(self._value)}) is not at least to {repr_(compare)}.",
+            self._not
+        )
+
+
+class AtMostComparisonInterface(NumberComparisonAssertionInterface):
+    def _compare(self) -> Assertion:
+        compare = self._generate_compare_to()
+        return Assertion(
+            self._value <= compare,
+            f"The value ({repr_(self._value)}) is not at least to {repr_(compare)}.",
+            self._not
+        )
+
+
+class EqualComparisonInterface(NumberComparisonAssertionInterface):
+    def _compare(self) -> Assertion:
+        compare = self._generate_compare_to()
+        return Assertion(
+            self._value == compare,
+            f"The value ({repr_(self._value)}) is not equal to {repr_(compare)}.",
+            self._not
+        )
+
+    @property
+    def to(self) -> Self:
+        return self
+
+
+class NumberInterface(AssertionInterface):
+    def __call__(self, value):
+        return EqualComparisonInterface(self._value, self)(value)
+
+    @property
+    def equals(self) -> EqualComparisonInterface:
+        return EqualComparisonInterface(self._value, self)
+
+    @property
+    def equal(self) -> EqualComparisonInterface:
+        return EqualComparisonInterface(self._value, self)
+
+    @property
+    def exactly(self) -> EqualComparisonInterface:
+        return EqualComparisonInterface(self._value, self)
+
+    @property
+    def of(self) -> EqualComparisonInterface:
+        return EqualComparisonInterface(self._value, self)
+
+    @property
+    def less_than(self) -> LessThanComparisonInterface:
+        return LessThanComparisonInterface(self._value, self)
+
+    @property
+    def more_than(self) -> MoreThanComparisonInterface:
+        return MoreThanComparisonInterface(self._value, self)
+
+    @property
+    def at_least(self) -> AtLeastComparisonInterface:
+        return AtLeastComparisonInterface(self._value, self)
+
+    @property
+    def at_most(self) -> AtMostComparisonInterface:
+        return AtMostComparisonInterface(self._value, self)
diff --git a/runtime-pyside6/tests/plugins/natural/interfaces/spy.py b/runtime-pyside6/tests/plugins/natural/interfaces/spy.py
new file mode 100644
index 0000000..524fd71
--- /dev/null
+++ b/runtime-pyside6/tests/plugins/natural/interfaces/spy.py
@@ -0,0 +1,218 @@
+"""
+ *  LogarithmPlotter - 2D plotter software to make BODE plots, sequences and distribution functions.
+ *  Copyright (C) 2021-2024  Ad5001
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program.  If not, see <https://www.gnu.org/licenses/>.
+"""
+
+from typing import Callable, Self
+
+from .base import Assertion, repr_, AssertionInterface
+from .int import NumberComparisonAssertionInterface
+
+PRINT_PREFIX = (" " * 3)
+
+
+class SpyAssertion(Assertion):
+    def __init__(self, assertion: bool, message: str, calls: list, invert: bool):
+        super().__init__(assertion, message + "\n", invert)
+        if len(calls) > 0:
+            self.message += self.render_calls(calls)
+        else:
+            self.message += f"{PRINT_PREFIX}0 registered calls."
+
+    def render_calls(self, calls):
+        lines = [f"{PRINT_PREFIX}{len(calls)} registered call(s):"]
+        for call in calls:
+            repr_args = [repr_(arg) for arg in call[0]]
+            repr_kwargs = [f"{key}={repr_(arg)}" for key, arg in call[1].items()]
+            lines.append(f"  - {', '.join([*repr_args, *repr_kwargs])}")
+        return ("\n" + PRINT_PREFIX).join(lines)
+
+
+class Methods:
+    AT_LEAST_ONCE = "AT_LEAST_ONCE"
+    EXACTLY = "EXACTLY"
+    AT_LEAST = "AT_LEAST"
+    AT_MOST = "AT_MOST"
+    MORE_THAN = "MORE_THAN"
+    LESS_THAN = "LESS_THAN"
+
+
+class CalledInterface(NumberComparisonAssertionInterface):
+    """
+    Internal class generated by Spy.called.
+    """
+
+    def __init__(self, calls: list[tuple[list, dict]], parent: AssertionInterface):
+        super().__init__(len(calls), parent)
+        self.__calls = calls
+        self.__method = Methods.AT_LEAST_ONCE
+
+    def __apply_method(self, calls):
+        required = None if self._compare_stack == [] else self._generate_compare_to()
+        calls_count = len(calls)
+        match self.__method:
+            case Methods.AT_LEAST_ONCE:
+                compare = len(calls) >= 1
+                error = f"Method was not called"
+            case Methods.EXACTLY:
+                compare = len(calls) == required
+                error = f"Method was not called {required} times ({required} != {calls_count})"
+            case Methods.AT_LEAST:
+                compare = len(calls) >= required
+                error = f"Method was not called at least {required} times ({required} >= {calls_count})"
+            case Methods.AT_MOST:
+                compare = len(calls) <= required
+                error = f"Method was not called at most {required} times ({required} <= {calls_count})"
+            case Methods.MORE_THAN:
+                compare = len(calls) > required
+                error = f"Method was not called more than {required} times ({required} > {calls_count})"
+            case Methods.LESS_THAN:
+                compare = len(calls) < required
+                error = f"Method was not called less than {required} times ({required} < {calls_count})"
+            case _:
+                raise RuntimeError(f"Unknown method {self.__method}.")
+        return compare, error
+
+    def __bool__(self) -> bool:
+        """
+        Converts to boolean on assertion.
+        """
+        compare, error = self.__apply_method(self.__calls)
+        return bool(SpyAssertion(compare, error + ".", self.__calls, self._not))
+
+    """
+    Chaining methods
+    """
+
+    def __call__(self, compare_to: int) -> Self:
+        super().__call__(compare_to)
+        if self.__method == Methods.AT_LEAST_ONCE:
+            self.__method = Methods.EXACTLY
+        return self
+
+    @property
+    def at_least(self) -> Self:
+        if self.__method == Methods.AT_LEAST_ONCE:
+            self.__method = Methods.AT_LEAST
+        else:
+            raise RuntimeError(f"Cannot redefine method from {self.__method} to {Methods.AT_MOST}")
+        return self
+
+    @property
+    def at_most(self) -> Self:
+        if self.__method == Methods.AT_LEAST_ONCE:
+            self.__method = Methods.AT_MOST
+        else:
+            raise RuntimeError(f"Cannot redefine method from {self.__method} to {Methods.AT_MOST}")
+        return self
+
+    @property
+    def more_than(self) -> Self:
+        if self.__method == Methods.AT_LEAST_ONCE:
+            self.__method = Methods.MORE_THAN
+        else:
+            raise RuntimeError(f"Cannot redefine method from {self.__method} to {Methods.MORE_THAN}")
+        return self
+
+    @property
+    def less_than(self) -> Self:
+        if self.__method == Methods.AT_LEAST_ONCE:
+            self.__method = Methods.LESS_THAN
+        else:
+            raise RuntimeError(f"Cannot redefine method from {self.__method} to {Methods.LESS_THAN}")
+        return self
+
+    @property
+    def time(self) -> Self:
+        return self
+
+    @property
+    def times(self) -> Self:
+        return self
+
+    """
+    Class properties.
+    """
+
+    def __match_calls_for_condition(self, condition: Callable[[list, dict], bool]) -> tuple[bool, str]:
+        calls = []
+        for call in self.__calls:
+            if condition(call[0], call[1]):
+                calls.append(call)
+        compare, error = self.__apply_method(calls)
+        return compare, error
+
+    def with_arguments(self, *args, **kwargs) -> SpyAssertion:
+        """
+        Checks if the Spy has been called the given number of times
+        with at least the given arguments.
+        """
+
+        def some_args_matched(a, kw):
+            args_matched = all((
+                arg in a
+                for arg in args
+            ))
+            kwargs_matched = all((
+                key in kw and kw[key] == arg
+                for key, arg in kwargs.items()
+            ))
+            return args_matched and kwargs_matched
+
+        compare, error = self.__match_calls_for_condition(some_args_matched)
+        repr_args = ', '.join([repr(arg) for arg in args])
+        repr_kwargs = ', '.join([f"{key}={repr(arg)}" for key, arg in kwargs.items()])
+        msg = f"{error} with arguments ({repr_args}) and keyword arguments ({repr_kwargs})."
+        return SpyAssertion(compare, msg, self.__calls, self._not)
+
+    def with_arguments_matching(self, test_condition: Callable[[list, dict], bool]) -> SpyAssertion:
+        """
+        Checks if the Spy has been called the given number of times
+        with arguments matching the given conditions.
+        """
+        compare, error = self.__match_calls_for_condition(test_condition)
+        msg = f"{error} with arguments matching given conditions."
+        return SpyAssertion(compare, msg, self.__calls, self._not)
+
+    def with_exact_arguments(self, *args, **kwargs) -> SpyAssertion:
+        """
+        Checks if the Spy has been called the given number of times
+        with all the given arguments.
+        """
+        compare, error = self.__match_calls_for_condition(lambda a, kw: a == args and kw == kwargs)
+        repr_args = ', '.join([repr(arg) for arg in args])
+        repr_kwargs = ', '.join([f"{key}={repr(arg)}" for key, arg in kwargs.items()])
+        msg = f"{error} with exact arguments ({repr_args}) and keyword arguments ({repr_kwargs})."
+        return SpyAssertion(compare, msg, self.__calls, self._not)
+
+    def with_no_argument(self) -> SpyAssertion:
+        """
+        Checks if the Spy has been called the given number of times
+        with all the given arguments.
+        """
+        compare, error = self.__match_calls_for_condition(lambda a, kw: len(a) == 0 and len(kw) == 0)
+        return SpyAssertion(compare, f"{error} with no arguments.", self.__calls, self._not)
+
+
+class SpyAssertionInterface(AssertionInterface):
+
+    @property
+    def called(self) -> CalledInterface:
+        """
+        Returns a boolean-able interface to check conditions for a given number of
+        time the spy was called.
+        """
+        return CalledInterface(self._value.calls, self)
diff --git a/runtime-pyside6/tests/plugins/natural/interfaces/utils.py b/runtime-pyside6/tests/plugins/natural/interfaces/utils.py
new file mode 100644
index 0000000..50e3777
--- /dev/null
+++ b/runtime-pyside6/tests/plugins/natural/interfaces/utils.py
@@ -0,0 +1,27 @@
+"""
+ *  LogarithmPlotter - 2D plotter software to make BODE plots, sequences and distribution functions.
+ *  Copyright (C) 2021-2024  Ad5001
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program.  If not, see <https://www.gnu.org/licenses/>.
+"""
+
+from PySide6.QtQml import QJSValue
+
+
+def repr_(data):
+    if isinstance(data, QJSValue):
+        variant = data.toVariant()
+        return f"QJSValue<{type(variant).__name__}>({repr(variant)})"
+    else:
+        return repr(data)
\ No newline at end of file
diff --git a/runtime-pyside6/tests/plugins/natural/spy.py b/runtime-pyside6/tests/plugins/natural/spy.py
new file mode 100644
index 0000000..2f9211a
--- /dev/null
+++ b/runtime-pyside6/tests/plugins/natural/spy.py
@@ -0,0 +1,33 @@
+"""
+ *  LogarithmPlotter - 2D plotter software to make BODE plots, sequences and distribution functions.
+ *  Copyright (C) 2021-2024  Ad5001
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program.  If not, see <https://www.gnu.org/licenses/>.
+"""
+from typing import Callable
+
+
+class Spy:
+    """
+    Class to spy into method calls with natural language expressions.
+    """
+
+    def __init__(self, function: Callable = None):
+        self.function = function
+        self.calls = []
+
+    def __call__(self, *args, **kwargs):
+        self.calls.append((args, kwargs))
+        if self.function is not None:
+            return self.function(*args, **kwargs)
diff --git a/runtime-pyside6/tests/plugins/natural/that.py b/runtime-pyside6/tests/plugins/natural/that.py
new file mode 100644
index 0000000..05a3e31
--- /dev/null
+++ b/runtime-pyside6/tests/plugins/natural/that.py
@@ -0,0 +1,68 @@
+"""
+ *  LogarithmPlotter - 2D plotter software to make BODE plots, sequences and distribution functions.
+ *  Copyright (C) 2021-2024  Ad5001
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program.  If not, see <https://www.gnu.org/licenses/>.
+"""
+from typing import overload, Generic, TypeVar
+
+from . import Spy
+from .interfaces.base import AssertionInterface, BaseAssertionInterface
+from .interfaces.basic import StringInterface, BoolInterface, ListInterface
+from .interfaces.int import NumberInterface
+from .interfaces.spy import SpyAssertionInterface
+
+Interface = TypeVar("Interface", bound=AssertionInterface)
+
+MATCHES = [
+    (str, StringInterface),
+    (bool, BoolInterface),
+    (int, NumberInterface),
+    (float, NumberInterface),
+    (list, ListInterface),
+    (Spy, SpyAssertionInterface)
+]
+
+
+@overload
+def that(value: str) -> StringInterface: ...
+
+
+@overload
+def that(value: bool) -> BoolInterface: ...
+
+
+@overload
+def that(value: int) -> NumberInterface: ...
+
+
+@overload
+def that(value: float) -> NumberInterface: ...
+
+@overload
+def that(value: Spy) -> SpyAssertionInterface: ...
+
+
+@overload
+def that[Interface](value: Interface) -> Interface: ...
+
+
+def that(value: any) -> AssertionInterface:
+    if not isinstance(value, AssertionInterface):
+        interface = next((i for t, i in MATCHES if isinstance(value, t)), None)
+        if interface is not None:
+            value = interface(value)
+        else:
+            value = BaseAssertionInterface(value)
+    return value
diff --git a/runtime-pyside6/tests/plugins/tests/__init__.py b/runtime-pyside6/tests/plugins/tests/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/runtime-pyside6/tests/plugins/tests/test_natural.py b/runtime-pyside6/tests/plugins/tests/test_natural.py
new file mode 100644
index 0000000..f381639
--- /dev/null
+++ b/runtime-pyside6/tests/plugins/tests/test_natural.py
@@ -0,0 +1,217 @@
+"""
+ *  LogarithmPlotter - 2D plotter software to make BODE plots, sequences and distribution functions.
+ *  Copyright (C) 2021-2024  Ad5001
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program.  If not, see <https://www.gnu.org/licenses/>.
+"""
+import pytest
+
+from ..natural import that, Assertion, Spy
+
+
+def test_string():
+    assert that("QWERTY").is_.an.instance_of(str)
+    assert that("QWERTY").is_.not_.an.instance_of(int)
+    assert that("QWERTY").is_.equal.to("QWERTY")
+    assert that("QWERTY").is_.NOT.equal.to("QWERTYUIOP")
+    assert that("QWERTY").is_.NOT.equal.to(3)
+    assert that("QWERTY").has.a.length.of(6)
+    assert that("QWERTY").does.NOT.have.a.length.of(7)
+    assert that("QWERTY").has.a.length.that.is_.NOT(5)
+    assert that("QWERTY").contains("WER")
+    assert that("QWERTY").contains("WER", "TY")
+    assert that("QWERTY").does.not_.contain("AZERTY")
+    with pytest.raises(Assertion):
+        assert that("QWERTY").is_.an.instance_of(int)
+    with pytest.raises(Assertion):
+        assert that("QWERTY").is_.equal.to(False)
+    with pytest.raises(Assertion):
+        assert that("QWERTY").has.a.length.of(1)
+    with pytest.raises(Assertion):
+        assert that("QWERTY").contains("AZERTY")
+    with pytest.raises(Assertion):
+        assert that("QWERTY").does.NOT.contain("QWE")
+
+def test_bool():
+    assert that(True).is_.an.instance_of(bool)
+    assert that(True).is_.an.instance_of(int)
+    assert that(True).is_.NOT.an.instance_of(str)
+    assert that(True).equals(True)
+    assert that(True).is_.true
+    assert that(True).is_.NOT.false
+    assert that(False).is_.equal.to(False)
+    assert that(False).is_.false
+    assert that(False).is_.NOT.true
+    with pytest.raises(Assertion):
+        assert that(True).is_.false
+    with pytest.raises(Assertion):
+        assert that(True).is_.NOT.true
+
+def test_int():
+    assert that(2).is_.an.instance_of(int)
+    assert that(2).is_.NOT.an.instance_of(bool)
+    assert that(2).is_.NOT.an.instance_of(str)
+    assert that(2).is_.more_than(1)
+    assert that(2).is_.NOT.less_than(1)
+    assert that(2).is_.less_than(3)
+    assert that(2).is_.NOT.more_than(3)
+    assert that(2).is_.at_least(1)
+    assert that(2).is_.NOT.at_most(1)
+    assert that(2).is_.at_most(3)
+    assert that(2).is_.NOT.at_least(3)
+    assert that(2).is_.at_most(2)
+    assert that(2).is_.at_least(2)
+    # Equality
+    assert that(2).is_(2)
+    assert that(2).was(2)
+    assert that(2).is_.exactly(2)
+    assert that(2).is_.equal.to(2)
+    assert that(2).equals(2)
+    assert that(2).is_.NOT(3)
+    assert that(2).does.NOT.equal(3)
+
+def test_int_shorthands():
+    # Direct numbers
+    assert that(0).equals.zero
+    assert that(1).equals.one
+    assert that(2).equals.two
+    assert that(3).equals.three
+    assert that(4).equals.four
+    assert that(5).equals.five
+    assert that(6).equals.six
+    assert that(7).equals.seven
+    assert that(8).equals.eight
+    assert that(9).equals.nine
+    assert that(10).equals.ten
+    assert that(11).equals.eleven
+    assert that(12).equals.twelve
+    assert that(13).equals.thirteen
+    assert that(14).equals.fourteen
+    assert that(15).equals.fifteen
+    assert that(16).equals.sixteen
+    assert that(17).equals.seventeen
+    assert that(18).equals.eighteen
+    assert that(19).equals.nineteen
+    assert that(20).equals.twenty
+    assert that(30).equals.thirty
+    assert that(40).equals.forty
+    assert that(50).equals.fifty
+    assert that(60).equals.sixty
+    assert that(70).equals.seventy
+    assert that(80).equals.eighty
+    assert that(90).equals.ninety
+    assert that(100).equals.a.hundred
+    assert that(1000).equals.a.thousand
+    assert that(1_000_000).equals.a.million
+
+def test_add_natural_complex():
+    # Test composed
+    assert that(34).equals.thirty.four
+    assert that(-34).equals.minus.thirty.four
+    assert that(100_033_207).equals.one.hundred.million.AND.thirty.three.thousand.AND.two.hundred.AND.seven
+    assert that(-1_200_033_207).equals.minus.one.billion.AND.two.hundred.million.AND.thirty.three.thousand.AND.two.hundred.AND.seven
+    assert that(7890).equals.seven.thousand.eight.hundred.and_.ninety
+    assert that(7890).equals.seventy.eight.hundred.and_.ninety
+    assert that(7890).equals(78)(100)(90)
+    with pytest.raises(RuntimeError):
+        assert that(1_000_000).equals.a.thousand.thousand
+    with pytest.raises(RuntimeError):
+        assert that(600).equals.one.twenty.thirty
+    with pytest.raises(RuntimeError):
+        assert that(2).equals
+    with pytest.raises(RuntimeError):
+        assert that(2).equals.one.minus.two
+
+def test_spy():
+    spy = Spy(lambda *args, **kw: 10)
+    assert that(spy).is_.an.instance_of(Spy)
+    assert that(spy).is_(callable)
+    # Check calls
+    assert that(spy).was.never.called
+    assert that(spy).was.called.zero.times
+    assert spy(30, arg="string") == 10
+    assert that(spy).was.called
+    assert that(spy).was.called.once
+    assert that(spy).was.called.one.time
+    assert that(spy).was.NOT.called.more_than.once
+    assert that(spy).was.called.with_arguments(30)
+    assert that(spy).was.called.with_arguments_matching(lambda args, kwargs: len(args) == 1 and len(kwargs) == 1)
+    assert that(spy).was.NOT.called.with_arguments(50)
+    assert that(spy).was.NOT.called.with_exact_arguments(30)
+    assert that(spy).was.NOT.called.with_no_argument()
+    assert that(spy).was.called.with_exact_arguments(30, arg="string")
+    with pytest.raises(Assertion):
+        assert that(spy).was.called.with_arguments(50)
+    with pytest.raises(Assertion):
+        assert that(spy).was.called.with_exact_arguments(30)
+    with pytest.raises(Assertion):
+        assert that(spy).was.called.with_no_argument()
+
+def test_spy_seral_calls():
+    spy = Spy()
+    obj = object()
+    spy()
+    spy(30, arg="string")
+    spy(obj, 30, example=obj, none=None)
+    assert that(spy).was.called
+    assert that(spy).was.called.more_than.once
+    assert that(spy).was.called.more_than.twice
+    assert that(spy).was.NOT.called.more_than.thrice
+    assert that(spy).was.called.at_most.thrice
+    assert that(spy).was.called.at_least.thrice
+    assert that(spy).was.called.three.times
+    assert that(spy).was.called.less_than(4).times
+    # Check arguments
+    assert that(spy).was.called.once.with_no_argument()
+    assert that(spy).was.called.at_most.once.with_no_argument()
+    assert that(spy).was.called.twice.with_arguments(30)
+    assert that(spy).was.NOT.called.less_than.twice.with_arguments(30)
+    assert that(spy).was.called.once.with_arguments(obj)
+    assert that(spy).was.called.once.with_arguments(arg="string")
+    assert that(spy).was.called.once.with_arguments(30, obj)
+    assert that(spy).was.called.once.with_arguments(none=None)
+    assert that(spy).was.NOT.called.with_arguments(None)
+    assert that(spy).was.NOT.called.with_arguments(obj, 30, arg="string")
+    with pytest.raises(Assertion):
+        assert that(spy).was.called.with_arguments(obj, 30, arg="string")
+    # Checking with exact arguments
+    assert that(spy).was.called.once.with_exact_arguments(30, arg="string")
+    assert that(spy).was.called.once.with_exact_arguments(obj, 30, example=obj, none=None)
+    assert that(spy).was.NOT.called.with_exact_arguments(obj, 30, arg="string")
+    with pytest.raises(Assertion):
+        assert that(spy).was.called.with_exact_arguments(obj, 30, arg="string")
+    # Check arguments matching
+    assert that(spy).has.NOT.been.called.with_arguments_matching(lambda a, kw: len(a) + len(kw) == 3)
+    assert that(spy).was.called.once.with_arguments_matching(lambda a, kw: len(a) + len(kw) == 2)
+    assert that(spy).was.called.once.with_arguments_matching(lambda a, kw: len(a) + len(kw) == 4)
+    with pytest.raises(Assertion):
+        assert that(spy).was.called.with_arguments_matching(lambda a, kw: len(a) + len(kw) == 3)
+
+
+def test_wrongful_expressions():
+    spy = Spy()
+    with pytest.raises(RuntimeError):
+        assert that(3).is_.less_than("str")
+    with pytest.raises(RuntimeError):
+        assert that(3).does.NOT.NOT.equal(3)
+    with pytest.raises(RuntimeError):
+        assert that(3).is_.an.instance_of("non type")
+    with pytest.raises(RuntimeError):
+        assert that(spy).was.called.more_than.at_least.once
+    with pytest.raises(RuntimeError):
+        assert that(spy).was.called.more_than.at_most.once
+    with pytest.raises(RuntimeError):
+        assert that(spy).was.called.more_than.less_than.once
+    with pytest.raises(RuntimeError):
+        assert that(spy).was.called.more_than.more_than.once
\ No newline at end of file
diff --git a/runtime-pyside6/tests/test_config.py b/runtime-pyside6/tests/test_config.py
index c919c6f..cef3673 100644
--- a/runtime-pyside6/tests/test_config.py
+++ b/runtime-pyside6/tests/test_config.py
@@ -1,3 +1,21 @@
+"""
+ *  LogarithmPlotter - 2D plotter software to make BODE plots, sequences and distribution functions.
+ *  Copyright (C) 2021-2024  Ad5001
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program.  If not, see <https://www.gnu.org/licenses/>.
+"""
+
 import pytest
 from LogarithmPlotter.util import config
 from tempfile import TemporaryDirectory
diff --git a/runtime-pyside6/tests/test_helper.py b/runtime-pyside6/tests/test_helper.py
index 5cfb239..6bc1f0d 100644
--- a/runtime-pyside6/tests/test_helper.py
+++ b/runtime-pyside6/tests/test_helper.py
@@ -30,7 +30,7 @@ from PySide6.QtWidgets import QApplication
 
 from LogarithmPlotter import __VERSION__ as version
 from LogarithmPlotter.util import config, helper
-from LogarithmPlotter.util.helper import Helper, InvalidFileException
+from LogarithmPlotter.util.helper import Helper, fetch_changelog, read_changelog, InvalidFileException
 
 pwd = getcwd()
 helper.SHOW_GUI_MESSAGES = False
@@ -60,19 +60,23 @@ CHANGELOG_BASE_PATH = path.realpath(path.join(path.dirname(path.realpath(__file_
 
 class TestHelper:
     def test_changelog(self, temporary, qtbot):
+        # Exists
         helper.CHANGELOG_VERSION = '0.5.0'
         tmpfile, directory = temporary
         obj = Helper(pwd, tmpfile)
         promise = obj.fetchChangelog()
         create_changelog_callback_asserter(promise, expect_404=False)
-        qtbot.waitSignal(promise.fulfilled, timeout=10000)
-        # No exist
+        with qtbot.waitSignal(promise.fulfilled, timeout=10000):
+            pass
+        assert type(fetch_changelog()) == str
+        # Does not exist
         helper.CHANGELOG_VERSION = '2.0.0'
         tmpfile, directory = temporary
         obj = Helper(pwd, tmpfile)
         promise = obj.fetchChangelog()
         create_changelog_callback_asserter(promise, expect_404=True)
-        qtbot.waitSignal(promise.fulfilled, timeout=10000)
+        with qtbot.waitSignal(promise.fulfilled, timeout=10000):
+            pass
         # Local
         tmpfile, directory = temporary
         obj = Helper(pwd, tmpfile)
@@ -81,7 +85,9 @@ class TestHelper:
         assert path.exists(helper.CHANGELOG_CACHE_PATH)
         promise = obj.fetchChangelog()
         create_changelog_callback_asserter(promise, expect_404=False)
-        qtbot.waitSignal(promise.fulfilled, timeout=10000) # Local
+        with qtbot.waitSignal(promise.fulfilled, timeout=100): # Local
+            pass
+        assert type(read_changelog()) == str
     
     def test_read(self, temporary):
         # Test file reading and information loading.
diff --git a/runtime-pyside6/tests/test_latex.py b/runtime-pyside6/tests/test_latex.py
index 6fd5c97..124186b 100644
--- a/runtime-pyside6/tests/test_latex.py
+++ b/runtime-pyside6/tests/test_latex.py
@@ -22,6 +22,7 @@ from shutil import which
 from os.path import exists
 from re import match
 from PySide6.QtGui import QColor
+from PySide6.QtQml import QJSValue
 
 from LogarithmPlotter.util import latex
 
@@ -38,10 +39,24 @@ def latex_obj():
     directory.cleanup()
 
 
+BLACK = QColor(0, 0, 0, 255)
+BLUE = QColor(128, 128, 255, 255)
+
+def check_render_results(result):
+    if isinstance(result, QJSValue):
+        result = result.toVariant()
+    assert type(result) == str
+    [path, width, height] = result.split(",")
+    assert exists(path)
+    assert match(r"\d+", width)
+    assert match(r"\d+", height)
+    return True
+
 class TestLatex:
     def test_check_install(self, latex_obj: latex.Latex) -> None:
         assert latex_obj.latexSupported == True
         assert latex_obj.checkLatexInstallation() == True
+        assert type(latex_obj.supportsAsyncRender) is bool
         bkp = [latex.DVIPNG_PATH, latex.LATEX_PATH]
         # Check what happens when one is missing.
         latex.DVIPNG_PATH = None
@@ -55,25 +70,25 @@ class TestLatex:
         [latex.DVIPNG_PATH, latex.LATEX_PATH] = bkp
 
     def test_render_sync(self, latex_obj: latex.Latex) -> None:
-        result = latex_obj.renderSync(r"\frac{d\sqrt{\mathrm{f}(x \times 2.3)}}{dx}", 14, QColor(0, 0, 0, 255))
+        result = latex_obj.renderSync("\\frac{d \\sqrt{\\mathrm{f}(x \\times 2.3)}}{dx}", 14, BLACK)
         # Ensure result format
-        assert type(result) == str
-        [path, width, height] = result.split(",")
-        assert exists(path)
-        assert match(r"\d+", width)
-        assert match(r"\d+", height)
+        check_render_results(result)
         # Ensure it returns errors on invalid latex.
         with pytest.raises(latex.RenderError):
-            latex_obj.renderSync(r"\nonexistant", 14, QColor(0, 0, 0, 255))
+            latex_obj.renderSync("\\nonexistant", 14, BLACK)
         # Replace latex bin with one that returns errors
         bkp = latex.LATEX_PATH
         latex.LATEX_PATH = which("false")
         with pytest.raises(latex.RenderError):
-            latex_obj.renderSync(r"\mathrm{f}(x)", 14, QColor(0, 0, 0, 255))
+            latex_obj.renderSync("\\mathrm{f}(x)", 14, BLACK)
+        # Replace latex bin with one goes indefinitely
+        latex.LATEX_PATH = which("import")
+        with pytest.raises(latex.RenderError):
+            latex_obj.renderSync("\\mathrm{f}(x)", 14, BLACK)
         latex.LATEX_PATH = bkp
 
     def test_prerendered(self, latex_obj: latex.Latex) -> None:
-        args = [r"\frac{d\sqrt{\mathrm{f}(x \times 2.3)}}{dx}", 14, QColor(0, 0, 0, 255)]
+        args = ["\\frac{d \\sqrt{\\mathrm{f}(x \\times 2.3)}}{dx}", 14, BLACK]
         latex_obj.renderSync(*args)
         prerendered = latex_obj.findPrerendered(*args)
         assert type(prerendered) == str
@@ -84,3 +99,27 @@ class TestLatex:
         prerendered2 = latex_obj.findPrerendered(args[0], args[1]+2, args[2])
         assert prerendered2 == ""
 
+    def test_render_async(self, latex_obj: latex.Latex, qtbot) -> None:
+        formula = "\\int\\limits^{3x}_{-\\infty}9\\mathrm{f}(x)^3+t dx"
+        og_promise = latex_obj.renderAsync(formula, 14, BLACK)
+        # Ensure we get the same locked one if we try to render it again.
+        assert og_promise == latex_obj.renderAsync(formula, 14, BLACK)
+        # Ensure queued renders.
+        promises = [
+            latex_obj.renderAsync(formula, 14, BLUE),
+            latex_obj.renderAsync(formula, 10, BLACK),
+            latex_obj.renderAsync(formula, 10, BLUE),
+        ]
+        for prom in promises:
+            assert og_promise.calls_upon_fulfillment(prom.start)
+        # Ensure other renders get done in parallel.
+        other_promise = latex_obj.renderAsync(formula+" dt", 10, BLACK)
+        assert not og_promise.calls_upon_fulfillment(other_promise.start)
+        # Ensure all of them render.
+        proms = [og_promise, *promises, other_promise]
+        with qtbot.waitSignals(
+            [p.fulfilled for p in proms],
+            raising=True, timeout=10000,
+            check_params_cbs=[check_render_results]*len(proms)
+        ):
+            pass
diff --git a/runtime-pyside6/tests/test_main.py b/runtime-pyside6/tests/test_main.py
index 047e21f..6b161ad 100644
--- a/runtime-pyside6/tests/test_main.py
+++ b/runtime-pyside6/tests/test_main.py
@@ -22,12 +22,13 @@ from os.path import exists, join
 from PySide6.QtGui import QIcon
 from tempfile import TemporaryDirectory
 
+from .globals import app
+
 from LogarithmPlotter.logarithmplotter import get_linux_theme, LINUX_THEMES, get_platform_qt_style, \
     register_icon_directories, install_translation, create_engine
 from LogarithmPlotter.util import config
 from LogarithmPlotter.util.helper import Helper
 from LogarithmPlotter.util.latex import Latex
-from globals import app
 
 THEMES = [
     "Basic",
diff --git a/runtime-pyside6/tests/test_native.py b/runtime-pyside6/tests/test_native.py
index 6fc2d65..3ca4834 100644
--- a/runtime-pyside6/tests/test_native.py
+++ b/runtime-pyside6/tests/test_native.py
@@ -17,7 +17,6 @@
 """
 
 import pytest
-from os.path import exists
 
 from PySide6.QtCore import QEvent, QObject, QUrl
 from PySide6.QtGui import QActionEvent, QFileOpenEvent
diff --git a/runtime-pyside6/tests/test_promise.py b/runtime-pyside6/tests/test_promise.py
new file mode 100644
index 0000000..30f0a1e
--- /dev/null
+++ b/runtime-pyside6/tests/test_promise.py
@@ -0,0 +1,177 @@
+"""
+ *  LogarithmPlotter - 2D plotter software to make BODE plots, sequences and distribution functions.
+ *  Copyright (C) 2021-2024  Ad5001
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program.  If not, see <https://www.gnu.org/licenses/>.
+"""
+from time import sleep
+
+import pytest
+from PySide6.QtQml import QJSValue
+
+from .plugins.natural import that, Spy
+from LogarithmPlotter.util.js import PyJSValue
+from LogarithmPlotter.util.promise import PyPromise
+
+
+def check_promise_result(value):
+    def got_result(args, kwargs, val=value):
+        valid = len(args) == 1 and len(kwargs) == 0
+        if valid:
+            got_value = args[0].toVariant() if isinstance(args[0], QJSValue) else args[0]
+            valid = got_value == val
+        return valid
+    return got_result
+
+def create_async_func(value):
+    def async_function(val=value):
+        sleep(1)
+        return val
+
+    return async_function
+
+
+def qjs_eq(origin):
+    def compare(result):
+        res = result.toVariant() == origin
+        print("Unknown res!", res, repr(result.toVariant()), repr(origin))
+        return res
+    return compare
+
+
+def async_throw():
+    sleep(1)
+    raise Exception("aaaa")
+
+
+class TestPyPromise:
+
+    def test_invalid_function(self):
+        with pytest.raises(ValueError):
+            promise = PyPromise("not a function")
+
+    def test_fulfill_values(self, qtbot):
+        qjsv = QJSValue(3)
+        values = [
+            [True, qjs_eq(True)],
+            [3, qjs_eq(3)],
+            [2.2, qjs_eq(2.2)],
+            ["String", qjs_eq("String")],
+            [qjsv, qjs_eq(3)],
+            [None, qjs_eq(None)],
+            [PyJSValue(QJSValue("aaa")), qjs_eq("aaa")]
+        ]
+        for [value, test] in values:
+            promise = PyPromise(create_async_func(value))
+            with qtbot.assertNotEmitted(promise.rejected, wait=1000):
+                with qtbot.waitSignal(promise.fulfilled, check_params_cb=test, timeout=2000):
+                    assert promise.state == "pending"
+            assert promise.state == "fulfilled"
+
+    def test_reject(self, qtbot):
+        promise = PyPromise(async_throw)
+        with qtbot.assertNotEmitted(promise.fulfilled, wait=1000):
+            with qtbot.waitSignal(promise.rejected, timeout=10000,
+                                  check_params_cb=lambda t: t == "Exception('aaaa')"):
+                assert promise.state == "pending"
+        assert promise.state == "rejected"
+
+    def test_fulfill(self, qtbot):
+        fulfilled = Spy()
+        rejected = Spy()
+        promise = PyPromise(create_async_func(3))
+        then_res = promise.then(fulfilled, rejected)
+        # Check if the return value is the same promise (so we can chain then)
+        assert that(then_res).does.equal(promise)
+        # Check on our spy.
+        with qtbot.waitSignal(promise.fulfilled, timeout=10000):
+                pass
+        assert that(fulfilled).was.called.once
+        assert that(fulfilled).was.NOT.called.with_arguments(3)
+        assert that(fulfilled).was.called.with_arguments_matching(check_promise_result(3))
+        assert that(rejected).was.never.called
+
+    def test_rejected(self, qtbot):
+        fulfilled = Spy()
+        rejected = Spy()
+        promise = PyPromise(async_throw)
+        then_res = promise.then(fulfilled, rejected)
+        # Check if the return value is the same promise (so we can chain then)
+        assert that(then_res).does.equal(promise)
+        # Check on our spies.
+        with qtbot.waitSignal(promise.rejected, timeout=10000):
+            pass
+        assert that(rejected).was.called.once
+        assert that(rejected).was.called.with_arguments("Exception('aaaa')")
+        assert that(fulfilled).has.never.been.called
+
+    def test_chain_fulfill(self, qtbot):
+        convert = Spy(lambda v: v.toVariant())
+        plus = Spy(lambda v: v + 1)
+        rejected = Spy()
+        promise = PyPromise(create_async_func(5))
+        then_res = promise.then(convert, rejected).then(plus, rejected).then(plus, rejected).then(plus, rejected)
+        # Check if the return value is the same promise (so we can chain then)
+        assert that(then_res).does.equal(promise)
+        with qtbot.waitSignal(promise.fulfilled, timeout=10000):
+            pass
+        assert that(convert).was.called.once.with_arguments_matching(check_promise_result(5))
+        assert that(rejected).was.never.called
+        assert that(plus).was.called.three.times
+        assert that(plus).was.called.once.with_exact_arguments(5)
+        assert that(plus).was.called.once.with_exact_arguments(6)
+        assert that(plus).was.called.once.with_exact_arguments(7)
+
+    def test_chain_reject(self, qtbot):
+        fulfilled = Spy()
+        convert = Spy(lambda v: len(v))
+        minus = Spy(lambda v: v - 1)
+        promise = PyPromise(async_throw)
+        then_res = promise.then(fulfilled, convert).then(fulfilled, minus).then(fulfilled, minus).then(fulfilled, minus)
+        # Check if the return value is the same promise (so we can chain then)
+        assert that(then_res).does.equal(promise)
+        with qtbot.waitSignal(promise.rejected, timeout=10000):
+            pass
+        assert that(fulfilled).was.never.called
+        assert that(convert).was.called.once.with_arguments_matching(check_promise_result("Exception('aaaa')"))
+        assert that(minus).was.called.three.times
+        assert that(minus).was.called.once.with_exact_arguments(17)
+        assert that(minus).was.called.once.with_exact_arguments(16)
+        assert that(minus).was.called.once.with_exact_arguments(15)
+
+    def test_check_calls_upon(self):
+        promise = PyPromise(async_throw)
+        fulfilled = Spy()
+        rejected = Spy()
+        promise.then(fulfilled, rejected)
+        assert promise.calls_upon_fulfillment(fulfilled)
+        assert promise.calls_upon_rejection(rejected)
+        assert not promise.calls_upon_fulfillment(rejected)
+        assert not promise.calls_upon_rejection(fulfilled)
+
+    def test_reject_in_fulfill(self, qtbot):
+        def fulfilled_throw(x):
+            raise Exception('noooo')
+        promise = PyPromise(create_async_func("3"))
+        fulfilled_throw = Spy(fulfilled_throw)
+        fulfilled = Spy()
+        rejected = Spy()
+        then_res = promise.then(fulfilled, rejected).then(fulfilled_throw, rejected).then(fulfilled, rejected).then(fulfilled, rejected)
+        # Check if the return value is the same promise (so we can chain then)
+        assert that(then_res).does.equal(promise)
+        with qtbot.waitSignal(promise.fulfilled, timeout=10000):
+            pass
+        assert that(fulfilled_throw).has.been.called.once
+        assert that(rejected).has.been.called.three.times
+        assert that(rejected).has.been.called.three.times.with_arguments("Exception('noooo')")
\ No newline at end of file
diff --git a/runtime-pyside6/tests/test_pyjs.py b/runtime-pyside6/tests/test_pyjs.py
index 5742cfc..95c3cf6 100644
--- a/runtime-pyside6/tests/test_pyjs.py
+++ b/runtime-pyside6/tests/test_pyjs.py
@@ -21,7 +21,6 @@ from re import Pattern
 from PySide6.QtQml import QJSEngine, QJSValue
 
 from LogarithmPlotter.util.js import PyJSValue, InvalidAttributeValueException, NotAPrimitiveException
-from globals import app
 
 @pytest.fixture()
 def data():
diff --git a/runtime-pyside6/tests/test_update.py b/runtime-pyside6/tests/test_update.py
index 5e1a705..ff71e61 100644
--- a/runtime-pyside6/tests/test_update.py
+++ b/runtime-pyside6/tests/test_update.py
@@ -49,19 +49,20 @@ def test_update(qtbot):
     update_info_newer = UpdateInformation()
     update_info_newer.got_update_info.connect(check_newer)
     runnable = UpdateCheckerRunnable('1.0.0', update_info_newer)
-    runnable.run()
-    qtbot.waitSignal(update_info_newer.got_update_info, timeout=10000)
+    with qtbot.waitSignal(update_info_newer.got_update_info, timeout=10000):
+        runnable.run()
     runnable = UpdateCheckerRunnable('0.1.0', update_info_older)
-    runnable.run()
-    qtbot.waitSignal(update_info_older.got_update_info, timeout=10000)
+    with qtbot.waitSignal(update_info_older.got_update_info, timeout=10000):
+        runnable.run()
     runnable = UpdateCheckerRunnable('0.5.0+dev0+git20240101', update_info_older)
-    runnable.run()
-    qtbot.waitSignal(update_info_older.got_update_info, timeout=10000)
+    with qtbot.waitSignal(update_info_older.got_update_info, timeout=10000):
+        runnable.run()
 
 def test_update_checker(qtbot):
     update_info = check_for_updates('0.6.0', MockWindow())
     assert QThreadPool.globalInstance().activeThreadCount() >= 1
-    qtbot.waitSignal(update_info.got_update_info, timeout=10000)
+    with qtbot.waitSignal(update_info.got_update_info, timeout=10000):
+        pass
     argv.append("--no-check-for-updates")
     update_info = check_for_updates('0.6.0', MockWindow())
     assert QThreadPool.globalInstance().activeThreadCount() < 2 # No new update checks where added
diff --git a/scripts/run-tests.sh b/scripts/run-tests.sh
index 1410244..8c09c54 100644
--- a/scripts/run-tests.sh
+++ b/scripts/run-tests.sh
@@ -1,8 +1,20 @@
 #!/bin/bash
 cd "$(dirname "$(readlink -f "$0" || realpath "$0")")/.." || exit 1
 
+box() {
+    len=${#1}
+    echo "┌─$(printf '─%.0s' $(seq 1 "$len"))─┐"
+    echo "│ $1 │"
+    echo "└─$(printf '─%.0s' $(seq 1 "$len"))─┘"
+}
+
 rebuild=true
 
+cd runtime-pyside6/tests/plugins || exit 1
+box "Testing pytest natural plugins..."
+PYTHONPATH="$PYTHONPATH:." pytest --cov=natural --cov-report term-missing .
+cd ../../../
+
 while [ $# -gt 0 ]; do
     case "$1" in
         --no-rebuild)
@@ -23,13 +35,16 @@ fi
 
 
 # Run python tests
+rm -rf build/runtime-pyside6/tests
 cp -r runtime-pyside6/tests build/runtime-pyside6
 cp -r ci CHANGELOG.md build/runtime-pyside6
 cd build/runtime-pyside6 || exit 1
+box "Testing runtime-pyside6..."
 PYTHONPATH="$PYTHONPATH:." pytest --cov=LogarithmPlotter --cov-report term-missing .
 cd ../../
 
 # Run js tests
 cd common || exit 1
+box "Testing common..."
 npm test