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173 lines
3.6 KiB
Markdown
173 lines
3.6 KiB
Markdown
# disallow large snapshots (`no-large-snapshots`)
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When using Jest's snapshot capability one should be mindful of the size of
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created snapshots. As a general best practice snapshots should be limited in
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size in order to be more manageable and reviewable. A stored snapshot is only as
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good as its review and as such keeping it short, sweet, and readable is
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important to allow for thorough reviews.
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## Usage
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Because Jest snapshots are written with back-ticks (\` \`) which are only valid
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with
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[ES2015 onwards](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Template_literals)
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you should set `parserOptions` in your config to at least allow ES2015 in order
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to use this rule:
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```js
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module.exports = {
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parserOptions: {
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ecmaVersion: 2015,
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},
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};
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```
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## Rule Details
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This rule looks at all Jest inline and external snapshots (files with `.snap`
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extension) and validates that each stored snapshot within those files does not
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exceed 50 lines (by default, this is configurable as explained in `Options`
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section below).
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Example of **incorrect** code for this rule:
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```js
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exports[`a large snapshot 1`] = `
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line 1
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`;
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```
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Example of **correct** code for this rule:
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```js
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exports[`a more manageable and readable snapshot 1`] = `
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line 1
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line 2
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line 3
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line 4
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`;
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```
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## Options
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This rule has options for modifying the max number of lines allowed for a
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snapshot:
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In an `eslintrc` file:
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```json
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{
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"rules": {
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"jest/no-large-snapshots": ["warn", { "maxSize": 12, "inlineMaxSize": 6 }]
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}
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}
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```
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Max number of lines allowed could be defined by snapshot type (Inline and
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External). Use `inlineMaxSize` for
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[Inline Snapshots](https://jestjs.io/docs/en/snapshot-testing#inline-snapshots)
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size and `maxSize` for
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[External Snapshots](https://jestjs.io/docs/en/snapshot-testing#snapshot-testing-with-jest).
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If only `maxSize` is provided on options, the value of `maxSize` will be used to
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both snapshot types (Inline and External).
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Since `eslint-disable` comments are not preserved by Jest when updating
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snapshots, you can use the `allowedSnapshots` option to have specific snapshots
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allowed regardless of their size.
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This option takes a map, with the key being the absolute filepath to a snapshot
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file, and the value an array of values made up of strings and regular
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expressions to compare to the names of the snapshots in the `.snap` file when
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checking if the snapshots size should be allowed.
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Note that regular expressions can only be passed in via `.eslintrc.js` as
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instances of `RegExp`.
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In an `.eslintrc.js` file:
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```javascript
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module.exports = {
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rules: {
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'jest/no-large-snapshots': [
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'error',
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{
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allowedSnapshots: {
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'/path/to/file.js.snap': ['snapshot name 1', /a big snapshot \d+/],
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},
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},
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],
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},
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};
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```
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Since absolute paths are typically not very portable, you can use the builtin
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`path.resolve` function to expand relative paths into absolutes like so:
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```javascript
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const path = require('path');
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module.exports = {
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rules: {
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'jest/no-large-snapshots': [
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'error',
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{
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allowedSnapshots: {
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[path.resolve('test/__snapshots__/get.js.snap')]: ['full request'],
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[path.resolve('test/__snapshots__/put.js.snap')]: ['full request'],
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},
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},
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],
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},
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};
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```
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