vibe-golden-file-testing

Golden file tests are powerful but brittle. This skill makes them robust.

When to Use This Skill

• Implementing tests that compare output against saved expected output
• Tests that currently break because dates, timestamps, or IDs change
• API response testing with dynamic fields
• CLI output testing

When NOT to Use This Skill

• Simple unit tests with static assertions
• Tests where the exact output IS the requirement (byte-for-byte)
• Performance benchmarks

The Problem

Golden tests break when they contain:

• Dates/timestamps (2026-02-28 → different tomorrow)
• UUIDs/IDs (random each run)
• Hostnames/ports (different per environment)
• File paths (absolute paths differ per machine)
• Durations (took 1.23s → varies by machine)

Steps

1. Identify dynamic fields in the output being tested

2. 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
   }
   

3. Apply normalization to BOTH:

   • The actual output (at test time)
   • The golden file (at generation time)

4. Generate golden file with update flag:

   if os.Getenv("UPDATE_GOLDEN") == "1" {
       os.WriteFile(goldenPath, normalized, 0644)
   }
   

5. Document update command:

   # To update golden files:
   UPDATE_GOLDEN=1 go test ./...
   

Common Normalizations

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

Output Format

Golden File Setup: [Test Name]

Dynamic fields found: X Normalizations applied: Y Golden file: [path] Update command: UPDATE_GOLDEN=1 [test command]