Implements snapshot/golden file tests with temporal normalization so tests don't break daily. Use when implementing tests that compare output against expected snapshots.
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Golden file tests are powerful but brittle. This skill makes them robust.
Golden tests break when they contain:
2026-02-28 → different tomorrow)took 1.23s → varies by machine)Identify dynamic fields in the output being tested
Create normalizer function:
func normalizeOutput(s string) string {
// Dates: 2026-02-28 → REDACTED_DATE
s = dateRegex.ReplaceAll(s, "REDACTED_DATE")
// UUIDs: 550e8400-... → REDACTED_UUID
s = uuidRegex.ReplaceAll(s, "REDACTED_UUID")
// Timestamps: 1709136000 → REDACTED_TS
s = tsRegex.ReplaceAll(s, "REDACTED_TS")
// Durations: 1.23s → REDACTED_DURATION
s = durationRegex.ReplaceAll(s, "REDACTED_DURATION")
return s
}
Apply normalization to BOTH:
Generate golden file with update flag:
if os.Getenv("UPDATE_GOLDEN") == "1" {
os.WriteFile(goldenPath, normalized, 0644)
}
Document update command:
# To update golden files:
UPDATE_GOLDEN=1 go test ./...
| Pattern | Regex | Replacement |
|---|---|---|
| ISO Date | \d{4}-\d{2}-\d{2} | REDACTED_DATE |
| ISO DateTime | \d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2} | REDACTED_DATETIME |
| UUID | [0-9a-f]{8}-[0-9a-f]{4}-... | REDACTED_UUID |
| Unix timestamp | \b1[6-9]\d{8}\b | REDACTED_TS |
| Duration | \d+\.?\d*[µnm]?s | REDACTED_DURATION |
| Absolute path | /home/\w+/ or C:\\Users\\ | REDACTED_PATH |
| Port | :\d{4,5}\b | :REDACTED_PORT |
Dynamic fields found: X
Normalizations applied: Y
Golden file: [path]
Update command: UPDATE_GOLDEN=1 [test command]
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Validates completed work against defined acceptance criteria. Use after completing a task that has specific success criteria defined in issues, specs, or task descriptions.
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Generates edge case, failure mode, and spec-driven test cases. Covers boundary values, nil inputs, concurrency, resource exhaustion, malformed data, and requirement-linked traceability tests. Use after happy-path tests exist and before claiming coverage is complete, when requirements lack tests, or before a security review.
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Catches shortcuts and reward hacking — weakening or deleting tests to make them pass, hard-coding expected outputs, silently dropping requirements, or claiming work is done without running it. Use before declaring a task complete and whenever a test or requirement feels like it's in the way.
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Safely integrates commits from parallel agent branches using sequential cherry-pick. Use after parallel work completes in isolated branches or worktrees.
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Audits tests for concurrency safety — race conditions, shared mock state, cleanup ordering. Use when writing tests that involve goroutines, async operations, or shared mutable state.
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Enforces tiered test coverage standards with three dimensions — line coverage by tier, spec-to-test traceability, and spec-to-code implementation mapping. Use before claiming code is complete.
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