Snapshot Tests
Did observable output change? Not “is it correct” but “did it change” — a sensor for detecting unintended drift in externally observable artifacts.
Snapshot tests (also called golden master or approval tests) record a canonical output and fail when it changes. They’re particularly useful when you don’t know what the correct output is, but you know it shouldn’t change without intention.
Sensor properties
| Property | Value |
|---|---|
| Oracle strength | Medium — change is detected, correctness is not |
| Independence | Low — same author creates the snapshot |
| Scope | Function-level |
| Feedback latency | Seconds |
| Actionability | Guiding — shows the diff between old and new output |
| Type | Predictive |
What it cannot detect
Snapshot tests can’t tell you whether the original snapshot was correct. They only detect change, not correctness. Also prone to “approve all” fatigue when outputs are large.