docs: add documentation on how to run tests

README.md

@@ -123,6 +123,49 @@ where `<qgis_plugins_path>` is one of:
 - Windows: `C:\Users\USER\AppData\Roaming\QGIS\QGIS3\profiles\default\python\plugins\ORStools`
 - Mac OS: `Library/Application Support/QGIS/QGIS3/profiles/default/python/plugins/ORStools`
 
+### CI
+#### Testing
+The repository tests on the QGis Versions *3.16*, *3.22* and the *latest* version. 
+Until now, it's only possible to test one version at a time.
+
+To do local test runs you can use a [conda installation](https://github.com/opengisch/qgis-conda-builder) of the QGis version you want to test.
+You will also have to install *xvfb* to run the tests on involving an interface. 
+Lastly, we need [*Pytest*](https://docs.pytest.org/en/8.0.x/) to run tests in general. 
+
+To do the above run use these commands:
+1. Install a version of anaconda, preferrably [*miniforge*](https://github.com/conda-forge/miniforge).
+
+2. Create and prepare the environment.
+```shell
+# create environment
+mamba create --name qgis_test
+# activate envotonment
+conda activate qgis_test
+# install pip
+mamba install qgis pip
+```
+3. Install QGis using mamba.
+```shell
+mamba install -c conda-forge qgis=[3.16, 3.22, latest] # choose one
+```
+
+4. Install *xvfb*
+```shell
+sudo apt-get update
+sudo apt install xvfb
+```
+
+5. Install *Pytest* using pip in testing environment.
+```shell
+pip install -U pytest
+```
+
+To run the tests you will need an ORS-API key:
+```shell
+cd orstools-qgis-plugin
+export ORS_API_KEY=[Your API key here] && xvfb-run pytest
+```
+
 ### Debugging
 In the **PyCharm community edition** you will have to use logging and printing to inspect elements.
 The First Aid QGIS plugin can probably also be used additionally.