[CAM-12931] Increase test coverage - camunda JIRA

Increase test coverage of the DMN engine (Scala DMN engine and Wrapper code)

Functionality tests for DMN elements should not be necessary (TCK runs fine)
Test coverage for edge cases not that high in general (e.g., type handling, incomplete user input)
Parsing edge cases are not covered much with tests
Existing DMN engine tests in the Platform should successfully run with Scala DMN (becomes more effort when JUEL is not supported with Scala DMN)
(Platform wrapper code should possibly receive a good coverage as well) [probably covered while implementing the wrapper code]

Increase test coverage of the DMN engine (Scala DMN engine and Wrapper code)

Functionality tests for DMN elements should not be necessary (TCK runs fine)
Test coverage for edge cases not that high in general (e.g., type handling, incomplete user input)
Parsing edge cases are not covered much with tests
Existing DMN engine tests in the Platform should successfully run with Scala DMN (becomes more effort when JUEL is not supported with Scala DMN)
(Platform wrapper code should possibly receive a good coverage as well) [probably covered while implementing the wrapper code]