Make tests fail gracefully if optional deps are missing

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 84.41%. Comparing base (6f053ff) to head (10ca0a7).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## mainline #557 +/- ## ============================================ - Coverage 84.48% 84.41% -0.07% ============================================ Files 71 71 Lines 6180 6180 Branches 518 518 ============================================ - Hits 5221 5217 -4 - Misses 959 963 +4 ```

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