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

Snapshot testing where new value can be a superset of the saved snapshot
https://github.com/bahmutov/subset-shot

ava jest mocha node nodejs qunit snapshot snapshot-testing subset

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Snapshot testing where new value can be a superset of the saved snapshot

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# subset-shot



> Snapshot testing where new value can be a superset of the saved snapshot



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



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

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

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



## Related



This is a sister project to [snap-shot](https://github.com/bahmutov/snap-shot) and

[schema-shot](https://github.com/bahmutov/schema-shot)



## Why



Imagine you have an API returning list of Oscar-winning movies. At some point it returns

N movie titles, including "Braveheart", "Titanic" and "The Artist" 

(see example page [here](http://www.today.com/popculture/complete-list-every-best-picture-oscar-winner-ever-t107617)).

You write an end to end test and would like to use 

[snapshot testing](https://facebook.github.io/jest/blog/2016/07/27/jest-14.html), but you cannot

because at some point in February of the next year a new movie will be added and your 

snapshot will have to be updated.



This module solves this problem by allowing *future values* to be a superset of the saved snapshot.

If API returns more movies - it is fine, as long as it returns all the ones already saved in the

snapshot.



## Install



Requires [Node](https://nodejs.org/en/) version 6 or above.



```sh

npm install --save-dev subset-shot

```



## Use



This module works using same [stack-walking, AST parsing magic](https://glebbahmutov.com/blog/snapshot-testing/)

as [snap-shot](https://github.com/bahmutov/snap-shot) and 

[schema-shot](https://github.com/bahmutov/schema-shot). This means, just use it in any testing

framework (like Ava, Jest, etc)



```js

// movies-spec.js

const subsetShot = require('subset-shot')

it('Oscar movies', () => {

  const list = ['Braveheart', 'Titanic']

  subsetShot(list)

})

```



The snapshot file will have contents



```js

// movies-spec.js.subset-shot

exports['Oscar movies'] = [

  'Braveheart', 

  'Titanic'

]

```



Later the API might return more movies, yet the same test still passes because the snapshot

has subset of the new data.



```js

// movies-spec.js

const subsetShot = require('subset-shot')

it('Oscar movies', () => {

  const list = ['Braveheart', 'Titanic', 'The Artist']

  subsetShot(list)

})

```



The test still passes. But a test that all of the sudden returns empty list or nothing, or

a totally different set of movies (by confusing "Best Picture" with "Best Director" for example)

fails.



## Updating snapshots



You can show the snapshots but skip saving them (dry run) by running tests with 

environment variable `DRY=1 npm test`.



You can show and save snapshots by running tests with environment variable `SHOW=1 npm test`.



You can update saved snapshots by running tests with environment variable `UPDATE=1 npm test`.



## Comparing objects



A snapshot could be an object subset, compared using 

[obj-subset](https://github.com/kvnneff/obj-subset).



```js

// saved snapshot is {foo: 42}

const subsetShot = require('subset-shot')

it('allows new properties', () => {

  subsetShot({foo: 42, bar: 10}) // ok

})

it('requires value', () => {

  subsetShot({foo: 20}) // exception, value should 42

})

it('requires matching key', () => {

  subsetShot({foo2: 42}) // exception, wrong key name

})

```



### Small print



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



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

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

* [blog](https://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/subset-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/subset-shot.svg?downloads=true

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

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

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