Avoid race condition crashes when handling duplicate classes #1926

All 1 523 tests pass, 1 skipped in 1m 2s

18 files ± 0 18 suites ±0 1m 2s ⏱️ ±0s
1 524 tests - 396 1 523 ✅ - 396 1 💤 ±0 0 ❌ ±0
2 536 runs ± 0 2 534 ✅ ± 0 2 💤 ±0 0 ❌ ±0

Results for commit 9f0dbda. ± Comparison against earlier commit fe081e8.