Fix test cases and create workflow for checking the tests

[GuentherJulian]

In the pull request #15 (comment) it was found that the test cases fail after changing the entity "Animal" to "Product". Probably that is why the test data in the xls files do not match anymore. This should be fixed. We should also add a workflow for testing the test cases, so that we see such errors directly in the pull request in the future.

[sobkowiak]

Tests should be run in the CI/CD workflow. Actually only mvn compile is used to build the source code

[GuentherJulian]

Closed with #20