Clean up some matrix helpers / test assertions #5139

All 775 tests pass, 2 skipped in 23m 55s

    1 files ±    0     1 suites +1 23m 55s ⏱️ + 23m 55s
777 tests +777 775 ✔️ +775 2 💤 +2 0 ❌ ±0
782 runs +782 780 ✔️ +780 2 💤 +2 0 ❌ ±0

Results for commit 6538ba3. ± Comparison against earlier commit 3af5d81.