This tutorial is part of our QGIS tutorial series:

• QGIS 3 Plugins - Plugin 101
• QGIS 3 Plugins - Qt Designer Explained
• QGIS 3 Plugins - Signals and Slots in PyQt
• QGIS 3 Plugins - Geocoding with Nominatim Part 1 (First Steps)
• QGIS 3 Plugins - Geocoding with Nominatim Part 2 (Interactivity)
• QGIS 3 Plugins - Geocoding with Nominatim Part 3 (Best Practices)
• QGIS 3 Plugins - Geocoding with Nominatim Part 4 (Tests & CI)
• QGIS 3 Plugins - Set up Plugin Repository
• QGIS 3 Plugins - Background Tasks

This tutorial is for now the last one in this series.

You'll follow up on the previous part, which introduced some best practices for QGIS plugin development and development in general. You can get the last tutorial's plugin code to follow along here, if you didn't actually go through it.

So, the final topic will be testing. Specifically we'll be looking at:

• unit
• e2e/integration tests
• set up Continuous Integration (CI) on GitHub

We'll go over the few different concepts over the course of writing tests. The final plugin can be found in our tutorial repository.

Big kudos to Mattheo Ghetta from Faunalia and Nyall Dawson from North Road for the testing setup of DataPlotly, where this tutorial got most of its inspiration from.

It can not be stressed enough: code breaks. It just does. With you, without you, even with und without you (the Schrödinger's you). QGIS evolves rapidly and sometimes deprecates existing functionality your code depends on. And of course you're human, so you actually do mistakes here and there. When you implement new features, there's no way you want to (or even can) test every single combination of user behavior. And you never really know what sort of side effects your changes might have on the rest of the code. This is where automated tests save the day (plus valuable developer time in the long run, horrible debugging pain and overwhelming user frustration).

Once you dig in you'll notice that the vast majority of QGIS plugins do not have automated test suites. (sad) Haftungsausschluss: I'm part of this vast majority too and this tutorial is a way out for me, and I hope provides some insight for you as well.

Having little test coverage on plugins should be a reason for concern, as bad user experience from buggy plugins could stain QGIS' reputation as a whole. I can't speak for the majority of plugin developers, but talking from my own experience this might be a result of:

• Little community guidelines
• Few properly implemented test suites in other plugins "to see how it's done"
• Sometimes authors are not professional developers and/or the plugin is a side project gone public with very limited time budgets (and testing is often lowest priority in that context)
• and last but not least: QGIS Plugins are hard(er) to test in all their components (GUI, processing, some async features etc)

In any case: this is a good example where majority behavior shouldn't be your guide. Dig in with us, it won't hurt (or not as much as you might fear 😉 I, for one, was very positively surprised!).

Goals:

• introduce basic unit tests
• learn e2e testing: how to test the UI the way a user interacts with the plugin
• set up a Github Actions workflow for the QGIS plugin so your code is tested when you push

Haftungsausschluss

Validity only confirmed for Linux und QGIS v3.18

• Basic understanding of Python
• QGIS v3.x
• Previous tutorial(s) or alternatively the prepared plugin
• Plugin Reloader plugin installed
• Python >= 3.6 (should be your system Python3)

As always in software development there are certain terms you should be familiar with (sigh..):

Unit testing ideally isolates each method to be tested individually, meaning no (or as little as possible) side effects from other parts of the code.
Integration tests ensure that the individual components work well together, e.g. the output of one function works as input to another function.
e2e tests imitate an actual user using the application for entire workflow start to finish.
CI stands for Continuous Integration and actually describes the behavior of merging code from several contributors on a regular basis. It's mostly synonymous today for running automated tests on a remote infrastructure. Here we'll use Github Actions.

Integration and e2e tests will be pretty much the same here, the lines are pretty blurry often anyways.

First we'll prepare our project. In the last tutorial we already took some measures to make the test-writing part a smooth(er) journey, so we don't actually have to touch any of the plugin code.

To not complicate things further we'll write our tests with Python's built-in unittest framework. In bigger projects, we usually prefer to use pytest, which uses an entirely different, more scalable approach.

We actually prefer to have out-of-source tests (i.e. in a root tests folder, so we don't have to ship irrelevant tests to users). However, the CI setup we'll come to later will depend on in-source tests. So create a folder called tests in quick_api/.

As a first action you'll copy/paste the code from smarter people than us, which will make the whole thing much easier.

Some background to that: One issue which makes testing QGIS plugins a little alien is the fact that we need to test software which is expecting to run within a QGIS application, but are run in isolated tests, i.e. not within the QGIS environment. You typically invoke unittest suites with python -m unittest from the command line. But then your code very much depends on a living QGIS environment, so you need a way to initialize one.

So, we copy some code from DataPlotly, which will set up QGIS and it's heavier components:

This one has been going around since the dawn of ages apparently (< QGIS v2) and is still highly useful.

It "mocks" (i.e. pretends to be) a QgisInterface. The real QgisInterface object is normally passed to your plugin in the root __init__.py by QGIS and can't be simply constructed in Python code to be usable. The mock defines a few stubs so that our plugin tests can use the "normal" QGIS functionality offered by QgisInterface, like adding toolbars, getting the QgsMapCanvas and so on.

Create this file in the quick_api/tests folder and copy the contents of the header link, we'll need it soon.

Only exposes a single function: get_qgis_app(). When called from outside a QGIS environment (as we do from our tests), this will set up and initialize a QGIS instance programmatically, so we can expect our plugin to work as expected.

It returns a tuple of:

• QGISAPP: The actual application object, i.e. a QgsApplication instance
• CANVAS: A clean QgsMapCanvas object initialized with size 400 x 400 px
• IFACE: The "mock" QgisInterface (see above)
• PARENT: A dummy QWidget() to act as parent for other widgets (not very useful)

With those objects we'll get very close to an actual QGIS environment. Close enough that our tests will succeed anyways.

So, create this file in the quick_api/tests folder and copy the contents of the header link, we'll need it soon.

In general, you'd want to have one test file per source file and test every single line/condition etc. It's important that you know what exactly to test for. You can get great test coverage yet not test a single important thing.

Let's first do the easy part and write a few tests for core/utils.py. Here we only have one single function, which serves two purposes: transforming a coordinate either from oder to WGS84. However, in the case where our project CRS is also WGS84, it shouldn't do anything and simply return the input point.

Create a file test_utils.py in quick_api/tests and paste the following:

import unittest

from qgis.core import QgsCoordinateReferenceSystem, QgsPointXY, QgsCoordinateTransform

from quick_api.core.utils import maybe_transform_wgs84


class TestUtils(unittest.TestCase):

    @classmethod
    def setUpClass(cls) -> None:
        cls.WGS = QgsCoordinateReferenceSystem.fromEpsgId(4326)
        cls.PSEUDO = QgsCoordinateReferenceSystem.fromEpsgId(3857)

    def test_to_wgs_pseudo(self):
        point = QgsPointXY(1493761.05913532, 6890799.81730105)
        trans_point = maybe_transform_wgs84(point, self.PSEUDO, QgsCoordinateTransform.ForwardTransform)
        self.assertEqual(trans_point, QgsPointXY(13.41868390243822162, 52.49867709045137332))

    def test_to_wgs_same_crs(self):
        point = QgsPointXY(13.41868390243822162, 52.49867709045137332)
        trans_point = maybe_transform_wgs84(point, self.WGS, QgsCoordinateTransform.ForwardTransform)
        self.assertEqual(trans_point, point)

It's conventional to prefix your test names with test_. In fact unittest will use this pattern to auto-discover your tests.

Here, we use the setUpClass() class method to initialize a few objects we'll need in the individual tests. This method will only run once before all its tests are executed and is often used to set up stuff like database connections etc. It has a counterpart called tearDownClass() which is run once after all its tests are executed. There's also setUp() und teardown() which are run before und after every test function, respectively.

Finally each test does some assert, which is the actual test. We advise you to use the unittest abstractions around assert (e.g. self.assertEqual()), otherwise the error messages on failures will be very non-descriptive.

Now you can run it with python -m unittest discover.

We "only" tested the cases for forward transformation, i.e. from EPSG:3857 to EPSG:4326. You can quickly make this more robust and test for the reverse transformations as well. Double-check with our solution.

Often you'll get away without initializing a full QGIS environment and can test just like we did above. However, sometimes you need to test code which relies on a QGIS environment and it's not always super obvious when that's the case.

To exemplify, let's test the Nominatim client in core/query.py. In the end there are only two scenarios we need to test here: a successful geocoding request and a failed one. So let's get to it:

import unittest

from qgis.core import QgsPointXY

from ..core.query import Nominatim


class TestNominatim(unittest.TestCase):
    """
    Test that Nominatim is returning valid results.
    """

    def _assertCoordsAlmostEqual(self, pt1: QgsPointXY, pt2: QgsPointXY, places=6):
        """Assert coordinates are the same within 0.000005 degrees"""
        self.assertAlmostEqual(pt1.x(), pt2.x(), places=places)
        self.assertAlmostEqual(pt1.y(), pt2.y(), places=places)

    def test_success(self):
        in_pt = QgsPointXY(13.395317, 52.520174)
        clnt = Nominatim()
        clnt.do_request(in_pt)

        self._assertCoordsAlmostEqual(in_pt, clnt.get_point(), places=4)

        expected_bbox = (QgsPointXY(13.3952203, 52.5201355), QgsPointXY(13.3953203, 52.5202355))
        list(map(lambda pts: self._assertCoordsAlmostEqual(*pts, places=4), zip(clnt.get_bbox_points(), expected_bbox)))

        address, license = clnt.get_attributes()
        self.assertIn('Am Kupfergraben', address)
        self.assertIn('OpenStreetMap contributors', license)

        self.assertEqual(clnt.status_code, 200)
        self.assertEqual(clnt.error_string, '')

    def test_failure(self):
        # test point in the Northern Sea
        in_pt = QgsPointXY(5.822754, 54.889246)
        clnt = Nominatim()
        clnt.do_request(in_pt)

        self.assertEqual(clnt.status_code, 200)  # Nominatim weirdness
        self.assertNotEqual(clnt.error_string, '')
        self.assertEqual(clnt.get_point(), None)
        self.assertEqual(clnt.get_bbox_points(), None)
        self.assertEqual(clnt.get_attributes(), None)

The tests should be pretty self-explanatory.

One problem with testing HTTP APIs like this is that we heavily rely on the actual response from Nominatim. That can be problematic because we don't have control over Nominatim's query results. Our test request might return a different response sometime in the future: the underlying OSM data could change, Nominatim could change its format etc. We do try to circumvent this issue a little by only comparing coordinates to 4 decimal places in self._assertCoordsAlmostEqual(). Often people "mock" HTTP API responses with e.g. responses. However, then the problem is again that we wouldn't be notified if Nominatim changes its request/response format which is even worse than a failing test here and there which we can easily correct when it happens.

If you run the tests now you should get an error along the lines of

[1]    43266 segmentation fault (core dumped)  python -m unittest`

What a useful error message.. So, what happened?

The issue is that the Nominatim class uses the QgsNetworkAccessManager class to make the request. And that one does depend on a QGIS environment: you can pass authentication strings from QGIS' auth database and it uses QGIS built-in proxy details if needed.

The solution couldn't be easier thanks to the effort of others: we simply have to import the get_qgis_app() function from quick_api/tests/utitlities and execute it at the top of the file which will initialize a QGIS instance and QgsNetworkAccessManager will have something to hold on to:

import unittest

from qgis.core import QgsPointXY

from ..core.query import Nominatim
from .utilities import get_qgis_app

QGIS_APP = get_qgis_app()


class TestNominatim(unittest.TestCase):
  ...

Now a python -m unittest discover will work!

This is much more interesting. Now we want to simulate a user's behavior and make sure the plugin reacts as intended. These sort of tests are often much more involved, because you often encounter parts of the Qt/QGIS API which are harder to test, such as modal dialogs, signals/slots etc.

For our little plugin, we have two e2e tests in mind:

1. The user has a project in a CRS different from WGS84, opens the plugin dialog, clicks in the map where Nominatim can find an address and the result will be dumped to a layer and added to the canvas.
2. The user does the same as in 1., but clicks in an area on the map where Nominatim will fail to find an address. In that case we want to make sure the modal error dialog is shown to the user before the plugin exits.

We'll only show the more interesting 2. scenario and you can add another method for yourself testing the 1. scenario (or look at our solution):

import unittest

from qgis.PyQt.QtTest import QTest
from qgis.PyQt.QtCore import Qt, QEvent, QPoint, QTimer
from qgis.PyQt.QtWidgets import QPushButton, QDialogButtonBox, QMessageBox, QApplication
from qgis.gui import QgsMapCanvas, QgsMapMouseEvent
from qgis.core import QgsProject, QgsCoordinateReferenceSystem, QgsRectangle, QgsVectorLayer, QgsFeature, \
    QgsFeatureIterator

from .utilities import get_qgis_app

# 1. Get all relevant QGIS objects
CANVAS: QgsMapCanvas
QGISAPP, CANVAS, IFACE, PARENT = get_qgis_app()


class TestFlow(unittest.TestCase):

    def test_full_failure(self):
        """Test failing request"""

        # 2. need to import here so that there's already an initialized QGIS app
        from quick_api.gui.quick_api_dialog import QuickApiDialog
        from quick_api.core.maptool import PointTool

        # 3. first set up a project
        CRS = QgsCoordinateReferenceSystem.fromEpsgId(3857)
        project = QgsProject.instance()
        CANVAS.setExtent(QgsRectangle(258889, 7430342, 509995, 7661955))
        CANVAS.setDestinationCrs(CRS)

        # 4. Create and open the dialog
        dlg = QuickApiDialog(IFACE)
        dlg.open()
        self.assertTrue(dlg.isVisible())

        # 5. Click the map button which should hide the dialog
        map_button: QPushButton = dlg.map_button
        QTest.mouseClick(map_button, Qt.LeftButton)
        self.assertFalse(dlg.isVisible())
        self.assertIsInstance(CANVAS.mapTool(), PointTool)

        # 6. Click in the map canvas, which should return the clicked coord,
        # make the dialog visible again
        map_releases = QgsMapMouseEvent(
            CANVAS,
            QEvent.MouseButtonRelease,
            QPoint(0, 0),  # Relative to the canvas' dimensions
            Qt.LeftButton,
            Qt.LeftButton,
            Qt.NoModifier
        )
        dlg.point_tool.canvasReleaseEvent(map_releases)
        self.assertRegex(dlg.lineedit_xy.text(), r'^(\d+\.\d+.+\d+\.\d+)$')
        self.assertTrue(dlg.isVisible())

        # 7. Clicking the OK button should result in a QMessageBox.critical dialog
        def handle_msgbox():
            msgbox: QMessageBox = QApplication.activeWindow()
            self.assertIsInstance(msgbox, QMessageBox)
            self.assertIn('Unable to geocode', msgbox.text())
            QTest.mouseClick(msgbox.button(QMessageBox.Ok), Qt.LeftButton)

        # Time the MsgBox test to 7000 ms after clicking
        # the OK button (Nominatim is rate limiting for ~6 secs..)
        QTimer.singleShot(7000, handle_msgbox)
        QTest.mouseClick(dlg.button_box.button(QDialogButtonBox.Ok), Qt.LeftButton)

        # 8. No layers produced
        layers = project.mapLayers(validOnly=True)
        self.assertEqual(len(layers), 0)

Let's go through point by point:

1. After all the imports you'll notice we capture all objects returned from get_qgis_app(). While the CANVAS is a real QgsMapCanvas object, IFACE is the stub class from qgis_interface.py which we'll need to initialize our own plugin dialog.
2. Next you'll see that we have another set of imports inside the test function. The reason here is that quick_api/core/maptool.py, from which PointTool is imported, defined a QPixMap as a static global variable. A QPixMap needs a running application apparently. If you stick to normal import patterns, Python would try to evaluate all the global and static stuff in the imported modules first, which is before get_qgis_app() is executed and will consequently fail. You can achieve the same if you import those two things after get_qgis_app() is called at the top of the file.
3. Then we set up the canvas to have a CRS of EPSG:3857 and set its extent to be somewhere in the Northern Sea to make sure Nominatim will definitely fail the request.
4. By creating the dialog with the fake QgisInterface (remember, we have no access to the real deal) we simulate the user opening the plugin dialog. The fake QgisInterface is also the reason why we create a QuickApiDialog and not the higher-level QuickApi class from quick_api/quick_api.py: the latter is only responsible to register some stuff with QGIS, mostly its iface member.
5. We can use QTest to simulate a left mouse click on the map_button (which is the name we gave this button in Qt Designer). QTest.mouseClick() will by default simulate the click in the center of the widget it's passed. Now we can test the expected behavior of hiding the plugin dialog and making sure our map tool is active.
6. The next step is a little tricky: We need to simulate that the user clicked (and released the click) on the map canvas. Remember our map tool has the canvasReleaseEvent() slot which is called with a QgsMapMouseEvent by QgsMapCanvas inside QGIS. QTest.mouseClick() cannot emit this event, so we have construct it ourselves and pass it to the map tool. That triggers our custom canvasClicked signal from quick_api/core/maptool.py which emits the transformed clicked point to the plugin dialog's lineedit_xy widget. A user would now see the dialog again with the WGS84 coordinates of the clicked point. We're not really caring about the exact Lat/Lon values since we don't have too much control which coordinate was clicked on the canvas, so we test with a simple regex.
7. This is the most interesting part. At this point the simulated user would only need to click "OK" to request Nominatim. But the request will fail, there are (almost) no addresses in the Northern Sea. On failure a modal dialog will open warning the user about it. A modal dialog is problematic because it stops code execution until the user interacts with it. However, in an automated test there is no user and once the modal dialog is open no one can push a button and the dialog would never close. To work around that Qt has a QTimer, which can schedule a task in the background before the modal dialog is triggered, passing the time in msec it should delay the execution of the passed function. So, 7 seconds after being called the QTimer.singleShot calls handle_msgbox() which will test that the modal dialog was indeed opened. We delay for 7 seconds because of Nominatim's quite heave rate limiting.
8. Finally we make sure there was no layer created.

When you run this test, don't be surprised when the message box pops up on your screen. It's supposed to. Don't interact with it (or any other window) as that would invalidate the test.

Testing our 1. scenario would look very similar: you'd choose a different area for the canvas' extent and check the created layer and the feature it contains. See our solution

Running all these tests is great, but how do we know our code was thoroughly tested? That's the job of the coverage package. First install it: pip install coverage. It's another tool we need to configure a little. In the pyproject.toml of the plugin include this section:

[tool.coverage.run]
branch = true
source = ["quick_api"]
omit = ["*/quick_api_dialog_base.py", "*/quick_api.py", '*/__init__.py', "*/tests/*", "*/test_suite.py"

This will only report the coverage of the quick_api package and omit files we don't want/need to test in that package.

Next we can run coverage run -m unittest discover && coverage report to print the coverage report to your console. While this is really helpful, it doesn't yet show you which parts of your code are not covered by tests. A coverage run -m unittest discover && coverage html will produce a htmlcov folder in your current directory. If you open the index.html in your web browser you'll be presented with an informative and interactive trace of your exact code coverage per module.

Finally we can set up our CI jobs on Github Actions, so you can get the fancy badges like . We won't give the full overview here for Github Actions as that's waaayyy out-of-scope. But there are a few peculiarities around testing QGIS plugins remotely, so we'll show you a little the ins and outs.

First look at the config YAML (needs to be in .github/workflows/<name>.yml):

name: Test plugin

auf:
  push:
    branches:
      - master
    paths:
      - "qgis/examples/quick_api_interactive_proper/**"
      - ".github/workflows/test_qgis_plugin.yaml"
  pull_request:
    branches:
      - master
    paths:
      - "qgis/examples/quick_api_interactive_proper/**"
      - ".github/workflows/test_qgis_plugin.yaml"

env:
  # plugin name/directory where the code for the plugin is stored
  PLUGIN_NAME: quick_api
  PLUGIN_PATH: qgis/examples/quick_api_interactive_proper_testing
  # python notation to test running inside plugin
  TESTS_RUN_FUNCTION: quick_api.test_suite.test_package

jobs:
  Tests:
    runs-on: ubuntu-latest
    strategy:
      matrix:
        docker_tags: [release-3_16, release-3_18, latest]
    steps:
      - name: Checkout
        uses: actions/checkout@v2
      - name: Docker pull and create container
        run: |
          docker pull qgis/qgis:${{ matrix.docker_tags }}
          docker run -d --name qgis-testing-environment -v "${GITHUB_WORKSPACE}/${PLUGIN_PATH}":/tests_directory -e DISPLAY=:99 qgis/qgis:${{ matrix.docker_tags }}
      - name: Docker set up QGIS
        run: |
          docker exec qgis-testing-environment sh -c "qgis_setup.sh $PLUGIN_NAME"
          docker exec qgis-testing-environment sh -c "rm -f /root/.local/share/QGIS/QGIS3/profiles/default/python/plugins/$PLUGIN_NAME"
          docker exec qgis-testing-environment sh -c "ln -s /tests_directory/$PLUGIN_NAME /root/.local/share/QGIS/QGIS3/profiles/default/python/plugins/$PLUGIN_NAME"
          docker exec qgis-testing-environment sh -c "pip3 install -r /tests_directory/requirements-tests.txt"
      - name: Docker run plugin tests
        run: |
          docker exec qgis-testing-environment sh -c "qgis_testrunner.sh $TESTS_RUN_FUNCTION"

One of the most important things to note here is the strategy matrix which defines docker tags for the relevant QGIS releases: LTR (3.16), stable (3.18) and latest (which is the master branch of QGIS). This strategy ensures that your plugin will work in the most relevant QGIS environments. Note, this obviously only tests Linux platforms, a setup for CI testing Windows and Mac could be worthwhile in case you include platform-specific stuff (like external, compiled libraries), but we have currently also no idea how to do that (future blog?).

The tests are run in a QGIS docker container, which contains some magic to set up the right environment. Just note for now, that your repository root is mapped to the /tests_directory directory inside the container.

One of the peculiarities with the above approach is that you'll need to provide a programmatic entrypoint for the tests; it can't execute the tests with python -m unittest. You can see in the last step it's calling qgis_testrunner.sh (provided by the QGIS image) with the argument $TESTS_RUN_FUNCTION aka quick_api.test_suite.test_package. That function doesn't exist yet, so let's create it in a new quick_api/test_suite.py file:

# coding=utf-8
import sys
import unittest
import qgis  # noqa: F401

import coverage
from osgeo import gdal

__author__ = 'Alessandro Pasotti'
__revision__ = '$Format:%H$'
__date__ = '30/04/2018'
__copyright__ = (
    'Copyright 2018, North Road')


def _run_tests(test_suite, package_name):
    """Core function to test a test suite."""
    count = test_suite.countTestCases()
    print('########')
    print('%s tests has been discovered in %s' % (count, package_name))
    print('Python GDAL : %s' % gdal.VersionInfo('VERSION_NUM'))
    print('########')

    cov = coverage.Coverage(
        source=['/tests_directory/quick_api'],
        omit=["*/quick_api_dialog_base.py", "*/quick_api.py", '*/__init__.py', "*/tests/*", "*/test_suite.py"],
    )
    cov.start()

    unittest.TextTestRunner(verbosity=3, stream=sys.stdout).run(test_suite)

    cov.stop()
    cov.save()
    cov.report(file=sys.stdout)


def test_package(package='quick_api'):
    """Test package.
    This function is called by travis without arguments.

    :param package: The package to test.
    :type package: str
    """
    test_loader = unittest.defaultTestLoader
    try:
        test_suite = test_loader.discover(package)
    except ImportError:
        test_suite = unittest.TestSuite()
    _run_tests(test_suite, package)


if __name__ == '__main__':
    test_package()

Now the CI command will programmatically invoke unittest und coverage, and print the report to the console.

Remember how we set up a linter (flake8) and style checker (black) in the last tutorial? Even though we already have a pre-commit hook to not push anything unlinted, we want to make sure any contributor's PR's are linted as well before merging them into master.

Add this section to your CI config yaml:

#jobs:
  ...

  Lint:
    runs-on: ubuntu-latest
    steps:

      - name: Install Python
        uses: actions/setup-python@v1
        with:
          python-version: '3.9'
          architecture: 'x64'

      - name: Checkout
        uses: actions/checkout@v2

      - name: Install packages
        run: |
          cd "${GITHUB_WORKSPACE}/${PLUGIN_PATH}" && pip install -r requirements-tests.txt

      - name: Flake8
        run: cd "${GITHUB_WORKSPACE}/${PLUGIN_PATH}" && flake8 .

      - name: Black
        run: cd "${GITHUB_WORKSPACE}/${PLUGIN_PATH}" && black . --check

Now the Lint job will fail if a PR or commit to master is not adhering to the project's style & lint constraints.

Now we have a couple of packages which our tests expect. These will have to be installed on the vanilla Python distribution that's typically installed on fresh Ubuntu CI machines.

Create the requirements-tests.txt file at the top level with the following:

coverage
black
flake8

The CI jobs we registered already take this requirements file into account.

Before pushing the new CI config YAML, make sure you test locally with one QGIS docker image. You can take most of the commands from the YAML as they are, but change the bits that need changing (e.g. environment variables).

Then you can finally push it and watch how CI is running your builds! Don't feel bad if you don't get it right on the first try. When I wrote this tutorial it took a solid 6 commits.