test: add missing asserts and fix mock return types

[alexander-held]

Fixing two things spotted in tests: the significance integration test was missing some asserts and the return types in a workspace building test should be dicts (but since this is all mocked, the test does not really change).

* add missing asserts to integration test
* fix return type of mock in workspace builder test

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (72e59dd) to head (34c0ac8).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##            master      #564   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           22        22           
  Lines         2132      2132           
  Branches       300       300           
=========================================
  Hits          2132      2132           

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