refactor for testability; add tests #1419

All 265 tests pass, 6 skipped in 10s

    1 files ±0     1 suites ±0 10s ⏱️ -1s
271 tests ±0 265 ✔️ ±0 6 💤 ±0 0 ❌ ±0
274 runs ±0 268 ✔️ ±0 6 💤 ±0 0 ❌ ±0

Results for commit 41cbed1. ± Comparison against earlier commit 3f3ba89.