μsnap

A micro snapshot testing tool that works very well with the Node >=18 built-in node:test harness.

Usage

npm install --save-dev usnap utap

Note: utap is of course optional: it is a test TAP output formatter.

my.test.js:

import snapshot from 'usnap';

snapshot.setup(import.meta.url);

test('test name', async t => {
  const obj = { foo: { bar: 42 } };

  await snapshot(obj, t.name);
});

Run the test:

node my.test.js | npx utap

The snapshot will be created in the snapshots/ directory next to my.test.js.

To update the snapshot:

node my.test.js -u | npx utap

But why?

• The currently built-in assert.snapshot is horrible since it is using util.inspect for serialization, with default options, which means limited depth and basically produces garbage.
• μsnap relies on YAML. One could not possibly choose a better format for snapshots, since it is
  • perfectly human-readable, git-friendly, and ubiquitously supported;
  • homomorphic in the sense

  assert.equal(YAML.stringify(array), array.map(a => YAML.stringify([a])).join(''))

  which makes it trivial to append to an existing snapshot file.
• Unlike most snapshot testing tools, μsnap creates a separate snapshot file for each individual test point. This avoids many issues when running tests in parallel and updating snapshots in --test-only mode.
• 60 lines of code with YAML as the only dependency.