Issues

• mutmut run crashes on float literals too large for a float, like 1e999

  boxed/mutmut#604 · Filter by author Ishaan400 opened on Oct 17, 2026

• Removing not from a parenthesized multi-line expression drops the parentheses (InvalidGeneratedSyntaxException, 3.8.0)

  boxed/mutmut#602 · Filter by author johnnywell opened on Oct 14, 2026

• Exception from the test run in a forked worker (wrongly) reports the mutant as killed

  boxed/mutmut#601 · Filter by author zyv opened on Oct 13, 2026

• Enums with custom __init__ cannot be imported under mutmut: KeyError: '_mutmut_orig'

  boxed/mutmut#600 · Filter by author zyv opened on Oct 13, 2026
  2

• Cross-call invalidation: changing a callee does not re-test mutants in its callers (3.8.0)

  boxed/mutmut#597 · Filter by author rocket-angel opened on Oct 12, 2026

• Stats collection crashes on Python 3.11 when a trampolined __del__ runs during GC (ContextVar re-entry)

  boxed/mutmut#596 · Filter by author yeongseon opened on Oct 11, 2026

• run with a name__mutmut_* pattern runs the whole test suite in the clean-test check

  boxed/mutmut#592 · Filter by author Chrisart27 opened on Oct 5, 2026
  1

• Mutating a typing.Protocol stub adds generated members to the Protocol and breaks type_check_command

  boxed/mutmut#590 · Filter by author GiulioDER opened on Oct 2, 2026
  2

• Generated trampoline names look like public members to tests that inspect classes (more visible since 3.8.0 mutates dataclasses)

  boxed/mutmut#586 · Filter by author kellyhair opened on Sep 26, 2026

• Process pools started by tests outlive every mutant (children end with os._exit() and share mutmut's process group)

  boxed/mutmut#584 · Filter by author m-groom opened on Sep 24, 2026

• Invalid unary plus generated in match statement

  boxed/mutmut#583 · Filter by author marten-de-vries opened on Sep 16, 2026

• mutmut breaks on tests with fixture directories with broken symlinks

  boxed/mutmut#582 · Filter by author juliancoffee opened on Sep 13, 2026
  3

• String mutations: the two case flips are equivalent wherever the consumer is case-insensitive, and no option turns them off

  enhancementgood first issue
  boxed/mutmut#577 · Filter by author MaxWolf-01 opened on Sep 9, 2026
  2

• What do the emoji's mean?

  boxed/mutmut#560 · Filter by author peekxc opened on Sep 2, 2026
  1

• mutate_only_covered_lines gates against stale line numbers on re-runs, silently dropping mutants

  boxed/mutmut#555 · Filter by author chwiese opened on Aug 23, 2026
  1

• Per-mutant timeout budget is parallelism-blind — full-core runs convert contention into spurious timeout verdicts

  boxed/mutmut#545 · Filter by author JonasPammerWork opened on Jul 31, 2026

• Exception: Could not find mutant for type error

  boxed/mutmut#541 · Filter by author nedbat opened on Jul 29, 2026
  6

• MutMut badge

  boxed/mutmut#536 · Filter by author cleder opened on Jul 9, 2026
  1

• (optionally) run the full test suite on any "surviving" mutants to confirm

  boxed/mutmut#535 · Filter by author ejfine opened on Jul 9, 2026
  3

• The pyrefly test fails

  boxed/mutmut#533 · Filter by author yurivict opened on Jun 28, 2026

• Copy lockfile (uv.lock/poetry.lock/…) alongside pyproject.toml into the mutants tree

  boxed/mutmut#529 · Filter by author ejfine opened on Jun 12, 2026
  7

• Support ty for filtering mutants

  boxed/mutmut#521 · Filter by author ejfine opened on Jun 4, 2026
  3

• Multi-page documentation

  documentation
  boxed/mutmut#507 · Filter by author Otto-AA opened on Apr 25, 2026
  1

• Using mutmut with Django: a working recipe (conftest + pyproject) — also closes the gap in #456

  boxed/mutmut#504 · Filter by author willianantunes opened on Apr 20, 2026
  3

• no example standard run Django tests with TestCase

  boxed/mutmut#503 · Filter by author ArtemIsmagilov opened on Apr 20, 2026
  4