Memoizing Tests

Vest introduces a new, top-level memo function. It allows you to cache parts of your suite execution based on dependencies, preventing unnecessary re-runs of expensive logic or async tests.

Why Memoize?

Validation suites often contain expensive operations, such as:

• Async checks: Checking if a username is taken (network request).
• Heavy computations: Validating complex data structures.

If the relevant data hasn't changed (e.g., the user is typing in the "password" field, but the "username" field hasn't changed), re-running the username check is wasteful. Memoization lets you skip these tests and reuse the previous result.

Unlike the previous test.memo which was limited to single tests, the new memo can wrap any part of your suite - single tests, multiple tests, groups, or arbitrary logic.

Usage

Import memo from vest:

import { create, test } from 'vest';
import { memo } from 'vest/memo';

const suite = create(data => {
  // cacheKey: [data.username]
  // If data.username hasn't changed since the last run,
  // this block is skipped, and previous results are restored.
  memo(() => {
    test('username', 'Username is taken', async () => {
      await checkAvailability(data.username);
    });
  }, [data.username]);
});

Memoizing Groups

You can use memo to skip entire groups of tests if their relevant data hasn't changed.

memo(() => {
  group('shipping_address', () => {
    test('street', 'Required', () => {
      /* ... */
    });
    test('city', 'Required', () => {
      /* ... */
    });
  });
}, [data.shipping_address]);

Advanced Configuration

memo accepts an optional third parameter: an options object to further control caching behavior.

memo(
  () => {
    test('username', 'Username is taken', async () => {
      await checkAvailability(data.username);
    });
  },
  [data.username],
  {
    cacheSize: 5, // Keep up to 5 previous results
    ttl: 10000, // Invalidate cache after 10 seconds
  },
);

Options

Option	Type	Default	Description
cacheSize	number	5	The maximum number of previous memo results to retain in the cache. When the limit is reached, the oldest result is evicted.
ttl	number	undefined	Time-to-Live in milliseconds. If the cached result is older than the ttl, the cache will be invalidated and the test blocked will be re-run.

How it works

1. Vest checks the dependency array passed as the second argument.
2. If the dependencies match the previous run, the callback function is not executed.
3. Instead, Vest restores the test results (pass/fail/warn) produced by that block in the previous run.