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https://github.com/bahmutov/snap-shot

Jest-like snapshot feature for the rest of us, works magically by finding the right caller function
https://github.com/bahmutov/snap-shot
jest jsx mocha react snapshot test unit-testing vue
Last synced: about 1 month ago
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Jest-like snapshot feature for the rest of us, works magically by finding the right caller function
Host: GitHub
URL: https://github.com/bahmutov/snap-shot
Owner: bahmutov
Created: 2017-01-31T04:34:29.000Z (almost 8 years ago)
Default Branch: master
Last Pushed: 2021-01-31T17:43:31.000Z (almost 4 years ago)
Last Synced: 2024-10-09T14:44:33.434Z (about 1 month ago)
Topics: jest, jsx, mocha, react, snapshot, test, unit-testing, vue
Language: JavaScript
Homepage:
Size: 200 KB
Stars: 168
Watchers: 2
Forks: 3
Open Issues: 18
Metadata Files:
- Readme: README.md
Awesome Lists containing this project

README

        # snap-shot

> Jest-like snapshot feature for the rest of us + data-driven testing!

**deprecated** please use [snap-shot-it][snap-shot-it] - it grabs test instance

at runtime, avoiding looking at the source code and getting lost in the transpiled code.

[snap-shot-it]: https://github.com/bahmutov/snap-shot-it

[![NPM][npm-icon] ][npm-url]

[![Build status][ci-image] ][ci-url]

[![semantic-release][semantic-image] ][semantic-url]

[![js-standard-style][standard-image]][standard-url]

[![status][link1]][url1] [snap-shot-jest-test](https://github.com/bahmutov/snap-shot-jest-test) - for testing `snap-shot` against Jest runner (React + JSX)

[![status][link2]][url2] [snap-shot-modules-test](https://github.com/bahmutov/snap-shot-modules-test) - for testing against transpiled ES6 modules

[![status][link3]][url3] [snap-shot-vue-test](https://github.com/bahmutov/snap-shot-vue-test) - for testing `snap-shot` inside Jest + Vue.js project

[![status][link4]][url4] [snap-shot-jsdom-test](https://github.com/bahmutov/snap-shot-jsdom-test) - for testing `snap-shot` using mock DOM adapter and element serialization

[![status][link5]][url5] [snap-shot-ava-test](https://github.com/bahmutov/snap-shot-ava-test) - for testing how `snap-shot` works with [Ava][ava] test framework

[link1]: https://travis-ci.org/bahmutov/snap-shot-jest-test.svg?branch=master

[url1]: https://travis-ci.org/bahmutov/snap-shot-jest-test

[link2]: https://travis-ci.org/bahmutov/snap-shot-modules-test.svg?branch=master

[url2]: https://travis-ci.org/bahmutov/snap-shot-modules-test

[link3]: https://travis-ci.org/bahmutov/snap-shot-vue-test.svg?branch=master

[url3]: https://travis-ci.org/bahmutov/snap-shot-vue-test

[link4]: https://travis-ci.org/bahmutov/snap-shot-jsdom-test.svg?branch=master

[url4]: https://travis-ci.org/bahmutov/snap-shot-jsdom-test

[link5]: https://travis-ci.org/bahmutov/snap-shot-ava-test.svg?branch=master

[url5]: https://travis-ci.org/bahmutov/snap-shot-ava-test

[ava]: https://github.com/avajs/ava

## Why

Read [Snapshot testing the hard way](https://glebbahmutov.com/blog/snapshot-testing/)

I like [Jest snapshot](https://facebook.github.io/jest/blog/2016/07/27/jest-14.html)

idea and want it without the rest of Jest testing framework. This module is

JUST a single assertion method to be used in BDD frameworks (Mocha, Jasmine)

Also, I really really really wanted to keep API as simple and as "smart"

as possible. Thus `snap-shot` tries to find the surrounding unit test name

by inspecting its call site

(using [stack-sites](https://github.com/bahmutov/stack-sites) or

[callsites](https://github.com/sindresorhus/callsites#readme))

and parsing AST of the spec file

(using [falafel](https://github.com/substack/node-falafel#readme)).

Snapshot values are compared using

[variable-diff](https://github.com/taylorhakes/variable-diff) (objects)

and [disparity](https://github.com/millermedeiros/disparity)

(multi line strings). See [images/README.md](images/README.md) for screenshots.

This function also includes [data-driven][data-driven] testing mode,

similar to [sazerac][sazerac], see [Data-driven testing](#data-driven-testing)

section below.

[data-driven]: https://hackernoon.com/sazerac-data-driven-testing-for-javascript-e3408ac29d8c#.9s4ikt67d

[sazerac]: https://github.com/mikec/sazerac

## Example

Install: `npm install --save-dev snap-shot`

```js

const snapshot = require('snap-shot')

// in ES6 code use

import snapshot from 'snap-shot'

it('is 42', () => {

  snapshot(42)

})

```

Run it first time with `mocha spec.js`.

This will create snapshots JSON values file inside

`__snapshots__/spec.js.snap-shot`.

In general this file should close to Jest format, but the file extension is

different to avoid clashing with Jest persistence logic.

```sh

$ mocha spec.js

$ cat __snapshots__/spec.js.snap-shot

module.exports[`is 42 1`] = 42

```

Now modify the `spec.js` file

```js

const snapshot = require('snap-shot')

it('is 42', () => {

  snapshot(80)

})

```

```sh

$ mocha spec.js

1) is 42:

    Error: expected 42 got 80

```

**Note** `snap-shot` does not store or handle `undefined` values, since they

are likely an edge case. If you disagree, open

[an issue](https://github.com/bahmutov/snap-shot/issues) please.

**Note** All values are saved as JSON, thus non-serializable values, like

functions are stripped before comparison.

## Promises

For asynchronous code, please have a function inside the spec before

calling `snap-shot` or let `snap-shot` wrap the promise.

```js

it('promise to function', () => {

  return Promise.resolve(20)

    .then(data => snapshot(data))

})

it('snap-shot can wrap promise', () => {

  return snapshot(Promise.resolve('value'))

})

// does NOT work

it('promise to snapshot', () => {

  return Promise.resolve(20)

    .then(snapshot)

})

```

In the last test, the stack trace from `snap-shot` cannot get any parent

information, thus it cannot find the unit test.

See [src/async-spec.js](src/async-spec.js)

## Jest

You can use this assertion inside Jest tests too.

```js

const snapshot = require('snap-shot')

test('my test', () => {

  snapshot(myValue)

})

```

## Ava

Should work (including `async / await` syntax), see

[snap-shot-ava-test](https://github.com/bahmutov/snap-shot-ava-test)

for the current status.

```js

import test from 'ava'

import snapshot from 'snap-shot'

test('concat strings', t => {

  snapshot('f' + 'oo')

})

```

## DOM testing (via jsdom and [jsdom-global][jsdom-global])

You can easily mock DOM and use snapshots (either in text or JSON format),

see [snap-shot-jsdom-test](https://github.com/bahmutov/snap-shot-jsdom-test)

project.

[jsdom-global]: https://github.com/rstacruz/jsdom-global

## React + JSX

If `snap-shot` finds `.babelrc` inside the current working folder, it will

try transpiling loaded files using

[babel-core](https://babeljs.io/docs/usage/api/) API. This makes it useful

for testing React code. For full example see

[Link.test.js](https://github.com/bahmutov/snap-shot-jest-test/blob/master/Link.test.js)

## Showing snapshots when saving

If you just want to see what a new schema would be, without saving it,

run the tests with `DRY=1 npm test` option.

If you want to see the schema and save it, run the tests with `SHOW=1 npm test`

```

$ SHOW=1 npm test

saving snapshot "spec name" for file ./src/valid-message-spec.js

{ firstLine: 'break(log): new log format',

  type: 'major',

  scope: 'log',

  subject: 'new log format'

}

```

## Update snapshots

To update all saved values, run with `UPDATE=1` environment variable.

```sh

$ UPDATE=1 mocha spec.js

```

To update snapshot inside a single test function, use second argument

```js

const snapshot = require('snap-shot')

it('is 42', () => {

  snapshot(80, true)

})

// snapshot file now has {"is 42": 80)

```

You can also update a single or several tests when running Mocha by filtering

the tests using [grep feature](http://mochajs.org/#g---grep-pattern).

```sh

$ UPDATE=1 mocha -g "test name pattern" *-spec.js

```

## CI

**Note** most CIs (like Travis, Circle, GitLabCI) define environment variable `CI`, which

we take into consideration as well. It makes no sense to allow saving snapshot on CI, thus if

the `process.env.CI` is set, the snapshot MUST exist on disk.

## Format

There is no magic in formatting snapshots. Just use any function or compose

with `snapshot` before comparing. Both choices work

```js

const snapshot = require('snap-shot')

it('compares just keys', () => {

  const o = {

    foo: Math.random(),

    bar: Math.random()

  }

  snapshot(Object.keys(o))

})

// snapshot will be something like

/*

exports['compares just keys 1'] = [

  "foo",

  "bar"

]

*/

const compose = (f, g) => x => f(g(x))

const upperCase = x => x.toUpperCase()

const upValue = compose(snapshot, upperCase)

it('compares upper case string', () => {

  upValue('foo')

})

/*

exports['compares upper case string 1'] = "FOO"

*/

```

See [src/format-spec.js](src/format-spec.js)

### General advice

Simple is better. Format the data and then call snapshot.

```js

it('works', () => {

  const domNode = ...

  const structure = formatHtml(domNode)

  snapshot(structure)

})

```

## Tests with dynamic names

Sometimes tests are generated dynamically without hardcoded names. In this

case SHA256 of the test callback function is used to find its value.

```js

// this still works

const testName = 'variable test name (value 30)'

const value = 30

it(testName, () => {

  // this is a test without hard coded name

  snapshot(value)

})

// snapshot file will have something like

// exports['465fb... 1'] = 30

```

The best strategy in this case is to use meaningful name for the callback

function

```js

const testName = 'variable test name (value 30)'

const value = 30

it(testName, function is30() {

  snapshot(value)

})

// snapshot file will have something like

// exports['is30 1'] = 30

```

See [src/unknown-name-spec.js](src/unknown-name-spec.js)

## Multiple snapshots

A single test can have multiple snapshots.

```js

it('handles multiple snapshots', () => {

  snapshot(1)

  snapshot(2)

})

it('uses counter of snapshot calls', () => {

  for (let k = 0; k < 10; k += 1) {

    snapshot(`snap ${k}`)

  }

})

```

See [src/multiple-spec.js](src/multiple-spec.js)

## Data-driven testing

Writing multiple input / output pairs for a function under test quickly

becomes tedious. Luckily, you can test a function by providing multiple

inputs and a single snapshot of function's *behavior* will be saved.

```js

// checks if n is prime

const isPrime = n => ...

it('tests prime', () => {

  snapshot(isPrime, 1, 2, 3, 4, 5, 6, 7, 8, 9)

})

```

The saved snapshot file will have clear mapping between given input and

produced result

```js

// snapshot file

exports['tests prime 1'] = {

  "name": "isPrime",

  "behavior": [

    {

      "given": 1,

      "expect": false

    },

    {

      "given": 2,

      "expect": true

    },

    {

      "given": 3,

      "expect": true

    },

    {

      "given": 4,

      "expect": false

    },

    {

      "given": 5,

      "expect": true

    },

    ...

  ]

}

```

You can also test functions that expect multiple arguments by providing

arrays of inputs.

```js

const add = (a, b) => a + b

it('checks behavior of binary function add', () => {

  snapshot(add, [1, 2], [2, 2], [-5, 5], [10, 11])

})

```

Again, the snapshot file gives clear picture of the `add` behavior

```js

// snapshot file

exports['checks behavior of binary function add 1'] = {

  "name": "add",

  "behavior": [

    {

      "given": [

        1,

        2

      ],

      "expect": 3

    },

    {

      "given": [

        2,

        2

      ],

      "expect": 4

    },

    {

      "given": [

        -5,

        5

      ],

      "expect": 0

    },

    {

      "given": [

        10,

        11

      ],

      "expect": 21

    }

  ]

}

```

See [src/data-driven-spec.js](src/data-driven-spec.js) for more examples.

## Debugging

Run with `DEBUG=snap-shot` environment variable

```sh

$ DEBUG=snap-shot mocha spec.js

```

If you want to see messages only when new values are stored use

```

$ DEBUG=save mocha spec.js

save Saved for "is 42 1" snapshot 42

```

There are special projects that are setup to test this code in isolation

as dependent projects, see above.

## Related

* [chai-jest-snapshot](https://github.com/suchipi/chai-jest-snapshot) if

  you are using [Chai](http://chaijs.com/)

* [schema-shot](https://github.com/bahmutov/schema-shot) - it is like snapshot

  testing but for dynamic data

  ([explanation](https://glebbahmutov.com/blog/schema-shot/))

### Small print

Author: Gleb Bahmutov <[email protected]> © 2017

* [@bahmutov](https://twitter.com/bahmutov)

* [glebbahmutov.com](http://glebbahmutov.com)

* [blog](http://glebbahmutov.com/blog)

License: MIT - do anything with the code, but don't blame me if it does not work.

Support: if you find any problems with this module, email / tweet /

[open issue](https://github.com/bahmutov/snap-shot/issues) on Github

## MIT License

Copyright (c) 2017 Gleb Bahmutov <[email protected]>

Permission is hereby granted, free of charge, to any person

obtaining a copy of this software and associated documentation

files (the "Software"), to deal in the Software without

restriction, including without limitation the rights to use,

copy, modify, merge, publish, distribute, sublicense, and/or sell

copies of the Software, and to permit persons to whom the

Software is furnished to do so, subject to the following

conditions:

The above copyright notice and this permission notice shall be

included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,

EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES

OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND

NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT

HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,

WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING

FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR

OTHER DEALINGS IN THE SOFTWARE.

[npm-icon]: https://nodei.co/npm/snap-shot.svg?downloads=true

[npm-url]: https://npmjs.org/package/snap-shot

[ci-image]: https://travis-ci.org/bahmutov/snap-shot.svg?branch=master

[ci-url]: https://travis-ci.org/bahmutov/snap-shot

[semantic-image]: https://img.shields.io/badge/%20%20%F0%9F%93%A6%F0%9F%9A%80-semantic--release-e10079.svg

[semantic-url]: https://github.com/semantic-release/semantic-release

[standard-image]: https://img.shields.io/badge/code%20style-standard-brightgreen.svg

[standard-url]: http://standardjs.com/