Understanding Results¶

Result categories¶

Every mutant gets one of these outcomes:

Killed mutants¶

A killed mutant means irradiate changed something (+ to -, and to or, etc.) and at least one test failed. No action needed.

Survived mutants¶

A survived mutant means irradiate changed something and all tests still passed. This is a gap.

irradiate show mylib.x_validate__irradiate_1

--- original
+++ mutant
 def validate(value):
-    if value > 0:
+    if value >= 0:
         return True

For each survivor, decide what to do. If the mutation represents a real bug your tests should catch, write a test. If the mutation is semantically equivalent in your context, add # pragma: no mutate to suppress it. Some survivors (e.g., n to n+1 in a non-critical index) may not warrant a test at all.

Timeouts¶

A timeout means the mutation created a non-terminating condition, like while cond: mutated to while True:. Timeouts count as killed because the mutation broke the program.

Mutation score¶

Score = killed / (killed + survived). Higher is better.

There's no universal threshold. Focus on survivors in code paths that handle important logic. A survived + to - in a pricing function is more concerning than one in a logging format string.

Viewing results¶

# Survived mutants only
irradiate results

# All mutants with status
irradiate results --all

# JSON output
irradiate results --json

# Inspect one mutant
irradiate show mylib.x_func__irradiate_1

Reports¶

# Stryker-compatible JSON
irradiate run --report json

# Self-contained HTML (opens in browser)
irradiate run --report html

In GitHub Actions, survived mutants appear as inline warning annotations on the PR diff.