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..3c2d223 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:
@@ -79,7 +77,7 @@ class PyPromise(QObject):
     Runs to_run in another thread, and calls fulfilled (populated by then) with its return value.
     """
     fulfilled = Signal((QJSValue,), (QObject,))
-    rejected = Signal(Exception)
+    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):
@@ -122,6 +120,35 @@ class PyPromise(QObject):
         if on_reject is not None:
             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)
diff --git a/runtime-pyside6/tests/spy.py b/runtime-pyside6/tests/spy.py
new file mode 100644
index 0000000..01f9aa0
--- /dev/null
+++ b/runtime-pyside6/tests/spy.py
@@ -0,0 +1,254 @@
+"""
+ *  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 PySide6.QtQml import QJSValue
+
+PRINT_PREFIX = (" " * 24)
+
+class SpyAssertionFailed(Exception):
+    def __init__(self, message, calls):
+        self.message = message + "\n"
+        if len(calls) > 0:
+            self.message += self.render_calls(calls)
+        else:
+            self.message += f"{PRINT_PREFIX}0 registered calls."
+
+    def repr(self, data):
+        if isinstance(data, QJSValue):
+            variant = data.toVariant()
+            return f"QJSValue<{type(variant).__name__}>({repr(variant)})"
+        else:
+            return repr(data)
+
+    def render_calls(self, calls):
+        lines = [f"{PRINT_PREFIX}{len(calls)} registered call(s):"]
+        for call in calls:
+            repr_args = [self.repr(arg) for arg in call[0]]
+            repr_kwargs =[f"{key}={self.repr(arg)}" for key, arg in call[1].items()]
+            lines.append(f"  - {', '.join([*repr_args, *repr_kwargs])}")
+        return ("\n" + PRINT_PREFIX).join(lines)
+
+    def __str__(self):
+        return self.message
+
+class Methods:
+    AT_LEAST_ONCE = "AT_LEAST_ONCE"
+    EXACTLY = "EXACTLY"
+    AT_LEAST = "AT_LEAST"
+    AT_MOST = "AT_MOST"
+    MORE_THAN = "AT_LEAST"
+    LESS_THAN = "AT_MOST"
+
+class CalledInterface:
+    """
+    Internal class generated by Spy.was_called.
+    """
+
+    def __init__(self, calls: list[tuple[list, dict]]):
+        self.__calls = calls
+        self.__method = Methods.AT_LEAST_ONCE
+        self.__times = None
+
+    def __apply_method(self, calls):
+        required = self.__times
+        calls_count = len(calls)
+        match self.__method:
+            case Methods.AT_LEAST_ONCE:
+                compare = len(calls) >= 1
+                error = "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):
+        """
+        Converts to boolean on assertion.
+        """
+        compare, error = self.__apply_method(self.__calls)
+        if not compare:
+            raise SpyAssertionFailed(error+".")
+        return compare
+
+
+    """
+    Chaining methods
+    """
+    def __call__(self, *args, **kwargs) -> Self:
+        if len(args) != 1:
+            raise RuntimeError("Cannot call called interface with more than one argument.")
+        self.__times = int(args[0])
+        if self.__method == Methods.AT_LEAST_ONCE:
+            self.__method = Methods.EXACTLY
+        return self
+
+    @property
+    def never(self) -> Self:
+        return self(0)
+
+    @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 at_least(self) -> Self:
+        self.__method = Methods.AT_LEAST
+        return self
+
+    @property
+    def at_most(self) -> Self:
+        self.__method = Methods.AT_MOST
+        return self
+
+    @property
+    def more_than(self) -> Self:
+        self.__method = Methods.MORE_THAN
+        return self
+
+    @property
+    def less_than(self) -> Self:
+        self.__method = Methods.LESS_THAN
+        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):
+        """
+        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)
+        if not compare:
+            repr_args = ', '.join([repr(arg) for arg in args])
+            repr_kwargs = ', '.join([f"{key}={repr(arg)}" for key, arg in kwargs.items()])
+            raise SpyAssertionFailed(f"{error} with arguments ({repr_args}) and keyword arguments ({repr_kwargs}).", self.__calls)
+        return compare
+
+
+    def with_arguments_matching(self, test_condition: Callable[[list, dict], bool]):
+        """
+        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)
+        if not compare:
+            raise SpyAssertionFailed(f"{error} with arguments matching given conditions.", self.__calls)
+        return compare
+
+
+    def with_exact_arguments(self, *args, **kwargs):
+        """
+        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)
+        if not compare:
+            repr_args = ', '.join([repr(arg) for arg in args])
+            repr_kwargs = ', '.join([f"{key}={repr(arg)}" for key, arg in kwargs.items()])
+            raise SpyAssertionFailed(f"{error} with exact arguments ({repr_args}) and keyword arguments ({repr_kwargs}).", self.__calls)
+        return compare
+
+    def with_no_argument(self):
+        """
+        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)
+        if not compare:
+            raise SpyAssertionFailed(f"{error} with no arguments.", self.__calls)
+        return compare
+
+
+
+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:
+            self.function(*args, **kwargs)
+
+    @property
+    def was_called(self) -> CalledInterface:
+        """
+        Returns a boolean-able interface to check conditions for a given number of
+        time the spy was called.
+        """
+        return CalledInterface(self.calls)
+
+    @property
+    def was_not_called(self) -> CalledInterface:
+        """
+        Returns a boolean-able interface to check that conditions were never fulfilled
+        in the times the spy was called.
+        """
+        ret = CalledInterface(self.calls)
+        return ret(0)
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_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..06c0b8a
--- /dev/null
+++ b/runtime-pyside6/tests/test_promise.py
@@ -0,0 +1,115 @@
+"""
+ *  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.QtCore import QObject
+from PySide6.QtQml import QJSValue
+
+from spy import 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_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):
+                print("Testing", value)
+                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):
+        spy_fulfilled = Spy()
+        spy_rejected = Spy()
+        promise = PyPromise(create_async_func(3))
+        then_res = promise.then(spy_fulfilled, spy_rejected)
+        # Check if the return value is the same promise (so we can chain then)
+        assert then_res == promise
+        # Check on our spy.
+        with qtbot.waitSignal(promise.fulfilled, timeout=10000):
+                pass
+        assert spy_fulfilled.was_called.once
+        assert spy_fulfilled.was_not_called.with_arguments(3)
+        assert spy_fulfilled.was_called.with_arguments_matching(check_promise_result(3))
+        assert spy_rejected.was_not_called
+
+    def test_rejected(self, qtbot):
+        spy_fulfilled = Spy()
+        spy_rejected = Spy()
+        promise = PyPromise(async_throw)
+        then_res = promise.then(spy_fulfilled, spy_rejected)
+        # Check if the return value is the same promise (so we can chain then)
+        assert then_res == promise
+        # Check on our spies.
+        with qtbot.waitSignal(promise.rejected, timeout=10000):
+            pass
+        assert spy_rejected.was_called.once
+        assert spy_rejected.was_called.with_arguments("Exception('aaaa')")
+        assert spy_fulfilled.was_not_called
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..ac1fdc5 100644
--- a/scripts/run-tests.sh
+++ b/scripts/run-tests.sh
@@ -23,6 +23,7 @@ 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