Improve test suites

[marcusolsson]

• gocheck helped when recreating the test cases from the original Java application but now's the time revisit, and rewrite them as stdlib tests instead.
• Many of the tests are using in-memory repositories. The tests should (where sense is made) instead be using the mock repositories from the mock package.

[marcusolsson]

Closed with 2e3f5358f9b58835aef4dbc4ab76902efc712918