avajs/ava · error · AssertionError

Did not match snapshot

Error message

Did not match snapshot

What it means

AVA throws this AssertionError from t.snapshot() when the snapshot engine returned a comparison result with result.pass === false and a result.actual descriptor — i.e. the snapshot file was read fine, but the value passed to t.snapshot() differs from the stored snapshot. AVA includes a formatted diff between the actual value and the expected snapshot in formattedDetails.

Source

Thrown at lib/assert.js:675

				const improperUsage = {assertion: 'snapshot', name: error.name, snapPath: error.snapPath};
				if (error instanceof VersionMismatchError) {
					improperUsage.snapVersion = error.snapVersion;
					improperUsage.expectedVersion = error.expectedVersion;
				}

				throw fail(new AssertionError(message ?? 'Could not compare snapshot', {
					asssertion: 't.snapshot()',
					improperUsage,
				}));
			}

			if (result.pass) {
				return pass();
			}

			if (result.actual) {
				throw fail(new AssertionError(message ?? 'Did not match snapshot', {
					assertion: 't.snapshot()',
					formattedDetails: [formatDescriptorDiff(result.actual, result.expected, {invert: true})],
				}));
			} else {
				// This can only occur in CI environments.
				throw fail(new AssertionError(message ?? 'No snapshot available — new snapshots are not created in CI environments', {
					assertion: 't.snapshot()',
				}));
			}
		});

		this.truthy = withSkip((actual, message) => {
			assertMessage(message, 't.truthy()');

			if (actual) {
				return pass();
			}

View on GitHub (pinned to bbfd946322)

Solutions

1. If the change is intentional, update snapshots with npx ava --update-snapshots and commit the .snap changes.
2. Inspect the formatted diff in the error details to decide whether the actual value or the snapshot is wrong; fix the code if the output regressed.
3. Remove stale entries or reorder t.snapshot() calls after refactoring tests so each call compares against the correct snapshot entry.
4. Normalize nondeterministic values (freeze time, seed randomness, round floats) before passing them to t.snapshot().

Example fix

// before
t.snapshot({updatedAt: new Date()}); // diff fails every run

// after
t.snapshot({updatedAt: 0}); // or use a fixed clock
// then: npx ava --update-snapshots

// Normalize nondeterministic values before snapshotting:
const stable = (value) => JSON.parse(JSON.stringify(value, (k, v) =>
  k === 'updatedAt' || k === 'id' ? '<normalised>' : v));
t.snapshot(stable(result), 'stable result');

When it happens

Trigger: Calling t.snapshot(value) where value serializes differently from the previously recorded snapshot for this test (same snapshot index/hotpath), e.g. changed output, changed key order or added fields, nondeterministic values (timestamps, random ids, floating point).

Common situations: A code change intentionally altered output but snapshots were not updated; inserting/removing a t.snapshot() call shifting snapshot indices so later assertions compare against wrong snapshots; environment-dependent output differing between dev and CI; locale/timezone differences affecting serialized values.

Related errors

• Cannot record snapshot ${index} for ${JSON.stringify(belongs
• `t.snapshot()` can only be used in tests
• The snapshot assertion message must be a non-empty string
• Could not compare snapshot
• No snapshot available — new snapshots are not created in CI

AI-assisted analysis of avajs/ava@bbfd946322 (2026-09-02). Data as JSON: /api/errors/86b9e377b4cf3f99. Report an issue: GitHub.