Jest Platform
You can use specific features of Jest as standalone packages by cherry picking them.
Below is a list of the available packages:
jest-changed-files
This is the tool for identifying modified files in a git/hg repository. It exports two functions:
- getChangedFilesForRoots will return a promise that resolves to an object with the changed files and repos.
- findRepos will return a promise that resolves to a set of repositories contained in the specified path.
Example
const {getChangedFilesForRoots} = require('jest-changed-files');
// prints the set of modified files since last commit in the current repo
getChangedFilesForRoots(['./'], {
lastCommit: true,
}).then(result => console.log(result.changedFiles));
jest-diff
The jest-diff is a tool for visualizing changes in data. It exports a function that compares two values of any type and will return a "pretty-printed" string illustrating the difference between the two arguments.
Example
const diff = require('jest-diff');
const a = {a: {b: {c: 5}}};
const b = {a: {b: {c: 6}}};
const result = diff(a, b);
// print diff
console.log(result);
jest-docblock
The jest-docblock is a tool for extracting and parsing the comments at the top of a JavaScript file. It exports various functions to manipulate the data inside the comment block.
Example
const {parseWithComments} = require('jest-docblock');
const code = `
/**
* This is a sample
*
* @flow
*/
console.log('Hello World!');
`;
const parsed = parseWithComments(code);
// will print an object with two attributes: comments and pragmas.
console.log(parsed);
jest-get-type
The jest-get-type is a module that identifies the primitive type of any JavaScript value. It exports a function that returns a string with the type of the value passed as argument.
Example
const getType = require('jest-get-type');
const array = [1, 2, 3];
const nullValue = null;
const undefinedValue = undefined;
// prints 'array'
console.log(getType(array));
// prints 'null'
console.log(getType(nullValue));
// prints 'undefined'
console.log(getType(undefinedValue));
jest-validate
This is a tool for validating configurations submitted by users. It will export a function that takes two arguments: one is the user's configuration and the other is an object containing an example configuration and other options. The return value is an object that has two attributes:
- hasDeprecationWarnings, a boolean that indicates whether the submitted configuration has deprecation warnings,
- isValid, a boolean that indicates whether the configuration is correct or not.
Example
const {validate} = require('jest-validate');
const configByUser = {
transform: '<rootDir>/node_modules/my-custom-transform',
};
const result = validate(configByUser, {
comment: ' Documentation: http://custom-docs.com',
exampleConfig: {transform: '<rootDir>/node_modules/babel-jest'},
});
console.log(result);
jest-worker
This is a module used for parallelization of tasks. It exports a class Worker that takes the path of Node.js module and allows you call the module's exported methods as if they were class methods, it will return a promise that resolves when the specified method finishes its execution in a forked process.
Example
// heavy-task.js
```module.exports = {
myHeavyTask: args => {
// long running CPU intensive task.
},
};```
// main.js
```async function main() {
const worker = new Worker(require.resolve('./heavy-task.js'));
// run 2 tasks in parallel with different arguments
const results = await Promise.all([
worker.myHeavyTask({foo: 'bar'}),
worker.myHeavyTask({bar: 'foo'}),
]);
console.log(results);
}
main();
pretty-format
This will export a function that converts any JavaScript value into a human-readable string. It supports all built-in JavaScript types out of the box and allows extension for application-specific types via user-defined plugins.
Example
const prettyFormat = require('pretty-format');
const val = {object: {}};
val.circularReference = val;
val[Symbol('foo')] ='foo';
val.map = new Map([['prop', 'value']]);
val.array = [-0, Infinity, NaN];
console.log(prettyFormat(val));
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