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# disallow large snapshots (`no-large-snapshots`)
When using Jest's snapshot capability one should be mindful of the size of
created snapshots. As a general best practice snapshots should be limited in
size in order to be more manageable and reviewable. A stored snapshot is only as
good as its review and as such keeping it short, sweet, and readable is
important to allow for thorough reviews.
## Usage
Because Jest snapshots are written with back-ticks (\` \`) which are only valid
with
[ES2015 onwards](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Template_literals)
you should set `parserOptions` in your config to at least allow ES2015 in order
to use this rule:
```js
module.exports = {
parserOptions: {
ecmaVersion: 2015,
},
};
```
## Rule Details
This rule looks at all Jest inline and external snapshots (files with `.snap`
extension) and validates that each stored snapshot within those files does not
exceed 50 lines (by default, this is configurable as explained in `Options`
section below).
Example of **incorrect** code for this rule:
```js
exports[`a large snapshot 1`] = `
line 1
line 2
line 3
line 4
line 5
line 6
line 7
line 8
line 9
line 10
line 11
line 12
line 13
line 14
line 15
line 16
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line 39
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line 50
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`;
```
Example of **correct** code for this rule:
```js
exports[`a more manageable and readable snapshot 1`] = `
line 1
line 2
line 3
line 4
`;
```
## Options
This rule has options for modifying the max number of lines allowed for a
snapshot:
In an `eslintrc` file:
```json
{
"rules": {
"jest/no-large-snapshots": ["warn", { "maxSize": 12, "inlineMaxSize": 6 }]
}
}
```
Max number of lines allowed could be defined by snapshot type (Inline and
External). Use `inlineMaxSize` for
[Inline Snapshots](https://jestjs.io/docs/en/snapshot-testing#inline-snapshots)
size and `maxSize` for
[External Snapshots](https://jestjs.io/docs/en/snapshot-testing#snapshot-testing-with-jest).
If only `maxSize` is provided on options, the value of `maxSize` will be used to
both snapshot types (Inline and External).
Since `eslint-disable` comments are not preserved by Jest when updating
snapshots, you can use the `allowedSnapshots` option to have specific snapshots
allowed regardless of their size.
This option takes a map, with the key being the absolute filepath to a snapshot
file, and the value an array of values made up of strings and regular
expressions to compare to the names of the snapshots in the `.snap` file when
checking if the snapshots size should be allowed.
Note that regular expressions can only be passed in via `.eslintrc.js` as
instances of `RegExp`.
In an `.eslintrc.js` file:
```javascript
module.exports = {
rules: {
'jest/no-large-snapshots': [
'error',
{
allowedSnapshots: {
'/path/to/file.js.snap': ['snapshot name 1', /a big snapshot \d+/],
},
},
],
},
};
```
Since absolute paths are typically not very portable, you can use the builtin
`path.resolve` function to expand relative paths into absolutes like so:
```javascript
const path = require('path');
module.exports = {
rules: {
'jest/no-large-snapshots': [
'error',
{
allowedSnapshots: {
[path.resolve('test/__snapshots__/get.js.snap')]: ['full request'],
[path.resolve('test/__snapshots__/put.js.snap')]: ['full request'],
},
},
],
},
};
```