adds informations how to run tests on the collection.

TESTING.md

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+## Collection Testing Guide
+
+This guide will quickstart you on our testing environment and eases the way to
+contribute on our project.
+
+### Tests
+
+Currently we do some molecule tests to check if the roles work in combination
+and some variables to check if anything fails.
+
+Then there are unit tests for the parser which generates the Icinga 2 DSL.
+
+At last we implemented a way to check if our Icingaweb roles generates valid
+ini files.
+
+### Tools
+
+Make sure the following tools are available before start testing with the collection.
+
+```
+pip install ansible-core ansible-lint molecule pytest-testinfra
+```
+
+To test roles locally without docker/service issues, we created a molecule test
+with vagrant. Then you need to install [vagrant](link/to/vagrant) and the molecule plugin.
+
+`pip install molecule-plugins[vagrant]`
+
+To use molecule with docker install the docker plugin.
+
+`pip install molecule-plugins[docker]`
+
+### Roles Testing
+
+To test roles over vagrant locally, it is the easiest to run the **local-default**
+scenario. The local-default is very big and long running. For shorter tests use
+the role-<rolename> scenarios.
+
+`molecule test -s local-default`
+
+The following tests are inplemented based on docker. Per default a **ubuntu2204**
+image from geerlingguy's container is used. Thanks [@geerlingguy Dockerhublink](https://hub.docker.com/u/geerlingguy)
+
+To test other distros use the command with the env **MOLECULE_DISTRO**.
+
+`MOLECULE_DISTRO=opensuseleap15 molecule test -s role-icingadb_redis`
+
+### Templating Tests
+
+The roles are generating configuration for Icingaweb2 and Icinga2 in various files.
+To ensure values are written to these files in right syntax we test those too.
+
+#### Python Unittest
+
+For testing our Icinga 2 objects syntax we implemented python unittests and try
+many combinations which occur in different python versions.
+
+For more information please have a look at the workflow `Python Unittest`.
+
+#### Icingaweb2 INI
+
+To test the INI configuration over Ansible in the Icinga Web 2 role, we implemented
+a molecule test to include the template from the role and test it with various values.