test-failure-investigator

Testing & Quality

Use when a test is failing and you need to determine root cause: is it flaky, an environment issue, or a real regression? Traces failure from symptom to fix.

QUICK START

How to use this skill

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Source SKILL.md: https://github.com/proffesor-for-testing/agentic-qe/blob/HEAD/.claude/skills/test-failure-investigator/SKILL.md

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Test Failure Investigator

Runbook-style skill for systematic test failure investigation. Given a failing test, determines root cause and recommends action.

Activation

/test-failure-investigator [test-name-or-file]

Investigation Flow

Step 1: Classify the Failure

Run the test 3 times and classify:

Result Pattern	Classification	Action
Fails consistently	Regression or Environment	Continue to Step 2
Fails intermittently	Flaky	Skip to Step 4
Passes now	Transient	Check CI logs, environment diff

# Run test 3 times
for i in 1 2 3; do npx jest {{test_file}} 2>&1 | tail -5; echo "--- Run $i ---"; done

Step 2: Narrow the Scope

# When did it start failing?
git log --oneline -20 -- {{related_source_files}}

# What changed recently?
git diff HEAD~5 -- {{related_source_files}}

# Does it fail in isolation?
npx jest {{test_file}} --testNamePattern="{{test_name}}"

# Does it fail with other tests?
npx jest --runInBand  # sequential execution

Step 3: Root Cause Analysis

Symptom	Likely Cause	Investigation
Timeout	Network/DB dependency	Check external service availability
Assertion mismatch	Logic change	Compare expected vs actual, check git blame
Import error	Dependency change	Check package.json changes, run `npm ci`
Permission denied	Environment	Check file permissions, Docker volumes
Out of memory	Resource leak	Profile with `--detectOpenHandles`

Step 4: Flaky Test Investigation

# Run 10 times to confirm flakiness
for i in $(seq 1 10); do npx jest {{test_file}} --forceExit 2>&1 | grep -E 'PASS|FAIL'; done

# Common flaky causes:
# - Shared state between tests (missing cleanup)
# - Time-dependent assertions (use fake timers)
# - Race conditions (missing await)
# - Port conflicts (use random ports)
# - Order dependency (run with --randomize)

Step 5: Report

## Test Failure Report
- **Test**: {{test_name}}
- **File**: {{test_file}}
- **Classification**: Regression / Flaky / Environment / Transient
- **Root Cause**: {{description}}
- **First Failed**: {{commit_hash}} ({{date}})
- **Fix**: {{recommended_action}}
- **Verified**: [ ] Fix applied and test passes 3x consecutively

Composition

After investigation, compose with:

/bug-reporting-excellence — if regression found, file a bug report
/regression-testing — if regression, add to regression suite
/qe-test-execution — for re-running tests after fix

Gotchas

Agent may guess at root cause without running the test — always reproduce first
"Works on my machine" is not a diagnosis — compare environments (node version, OS, deps)
Flaky tests that pass 9/10 times will still be reported as "passing" by CI — run 10+ times
Test isolation failures are the #1 cause of flaky tests — check for shared state in beforeAll/afterAll