test_optimization: print set of tested solvers

[codecov[bot]]

Codecov Report

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

Project coverage is 89.03%. Comparing base (9656735) to head (9471489). Report is 15 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #252 +/- ## ========================================== + Coverage 85.86% 89.03% +3.17% ========================================== Files 15 15 Lines 3572 3640 +68 Branches 836 852 +16 ========================================== + Hits 3067 3241 +174 + Misses 393 277 -116 - Partials 112 122 +10 ```

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