Improve test coverage

[MartinBenediktBusch]

Test Coverage Status Quo:

To Do

• Make tests independent of the default seed as described here Add parameters to seed #335
• Create test cases for services that do not have any test yet
• Push test coverage of functions (% Func) to 100% (i.e. each function should at least have one test case).
• Push overall percentage (row: all files) of Statements (% Stmts) and Lines (% Lines) to >= 80 %