Snap

Snap is a test snapshot library for Deno. modified from klick.

Features:

• Two update modes:
  1. update fine grained update (only filtered tests, even within a single suite)
  2. refresh coarse grained update (removes un-exercised snapshots within suites)
• Simple ability to mask variant fields, accessed via json-ptr
• CI aware - does not update snapshots on CI server
• Snapshot files are valid JSON5

Required Permissions

In practice, we'll need to use this:

• --allow-read: to read snapshots
• --allow-write: to create/update snapshots
• --unstable: for fs capability from deno std-lib

Current deno implementation does not allow for wild-cards and globs in the permissions allow-list. Ideally, this is the set of permissions snap needs:

• --allow-read="./**/*.assertSnapshot": to read snapshots
• --allow-write="./**/*.assertSnapshot": to create/update snapshots
• --unstable: for fs capability from deno std-lib

Usage

Writing tests

import test from "https://deno.land/x/snap/mod.ts";

test(`Simple test`, ({ assertSnapshot}) => {
  const actual = {
    a: 'a',
    b: 1
  }
  assertSnapshot(actual);
  actual.c = 'c'
  assertSnapshot(actual);
});

test(`Test with masks`, ({ assertSnapshot}) => {
  const actual = {
    a: 'a',
    b: 1,
    c: {
      start: Date.now()
      randomArray:  [
        Math.random(),
        Math.random(),
      ]
    }
  }
  const masks = ['/c/start', '/c/randomArray/*']
  assertSnapshot(actual, masks);
});

Masked snapshot:

'Test with masks': {
    a: 'a',
    b: 1,
    c: {
      start: '[MASKED number]',
      randomArray: [
        '[MASKED number]',
        '[MASKED number]',
      ],
    },
  },

Snapshot Management (Exercise from CLI)

New snapshots / Validate

Validate existing snapshots or create new snapshots

deno test --allow-write --allow-read --unstable

Filtered snapshot update

Only updates snapshots for tests being executed. Honors ignore and only attributes from Deno.TestDefinition

deno test --allow-write --allow-read --unstable --filter "/.*another.*/" -- --update

or

deno test --allow-write --allow-read --unstable --filter "/.*another.*/" -- --u

Refresh snapshots

Update all snapshots, deleting any un-executed snapshots. Only does so if a test-suite is executed

deno test --allow-write --allow-read --unstable -- --refresh

or

deno test --allow-write --allow-read --unstable -- --r