Add tests for stages cohabitation

[Drarig29]

Write tests to check that it's correctly working when multiple stages exist in the storage.

[Drarig29]

This should already work because everything is based on ids. However, tests are written in the assumption that there is only one stage in the storage.

Example:

assert.equal((await storage.select('group')).length, 1);
assert.equal((await storage.select('round')).length, 4);
assert.equal((await storage.select('match')).length, 15);