Write test for 'MetaProperty.hashCode'

[nipafx]

The method MetaProperty.hashCode() is currently not tested. This issue can be resolved by ...

• ... writing meaningful tests or
• ... coming to the conclusion that no tests are necessary / reasonable, in which case this should be documented in the test class

The corresponding ToDo should be removed.

Some Pointers

A short discussion about what a test could look like can be found here.

Tests should be added to AbstractMetaPropertyTest if possible. It might make sense to take a look at the tests for equals() which use a special mock to ensure that only defined fields are used for equality comparison.

(The links above point to a specific version and should be compared to the current version before starting to work on this issue.)