0b5982b9

By: Tom Sydney Kerckhove <syd@cs-syd.eu>

Abort mutation run when coverage baseline tests fail

When a coverage child observes a test failure during baseline collection,
mutation testing against that suite would produce meaningless scores —
the test was already red before any mutation ran.

The coverage child now prints the offending test's output and a loud
warning whenever a baseline test fails. Under --mutation-fail-fast it
additionally exits with code 2; the parent treats that as a non-retryable
abort signal, cancels the remaining workers via a new CoverageFailFast
exception (distinct from the existing MutationFailFast used for survivors
and uncovered mutations), and exits non-zero.

The fail-fast value is forwarded to coverage children explicitly so the
child's behaviour follows the parent's setting rather than its own default.

Timeline