npm package discovery and stats viewer.

Discover Tips

  • General search

    [free text search, go nuts!]

  • Package details

    pkg:[package-name]

  • User packages

    @[username]

Sponsor

Optimize Toolset

I’ve always been into building performant and accessible sites, but lately I’ve been taking it extremely seriously. So much so that I’ve been building a tool to help me optimize and monitor the sites that I build to make sure that I’m making an attempt to offer the best experience to those who visit them. If you’re into performant, accessible and SEO friendly sites, you might like it too! You can check it out at Optimize Toolset.

About

Hi, 👋, I’m Ryan Hefner  and I built this site for me, and you! The goal of this site was to provide an easy way for me to check the stats on my npm packages, both for prioritizing issues and updates, and to give me a little kick in the pants to keep up on stuff.

As I was building it, I realized that I was actually using the tool to build the tool, and figured I might as well put this out there and hopefully others will find it to be a fast and useful way to search and browse npm packages as I have.

If you’re interested in other things I’m working on, follow me on Twitter or check out the open source projects I’ve been publishing on GitHub.

I am also working on a Twitter bot for this site to tweet the most popular, newest, random packages from npm. Please follow that account now and it will start sending out packages soon–ish.

Open Software & Tools

This site wouldn’t be possible without the immense generosity and tireless efforts from the people who make contributions to the world and share their work via open source initiatives. Thank you 🙏

© 2024 – Pkg Stats / Ryan Hefner

jest-nest

v2.2.3

Published

jest mock for curried and chained functions

Downloads

52

Readme

codecov snyk npm version

jest-nest

Jest mocks for curried, chained functions and nested objects

  • Create mock for curried function with any number of parameters
  • Create mock for chained function of any depth
  • Create mock for objects that return (deeply) nested objects and specify return values at any path
  • Easy to use expectation

With this you can write:

const mock = nest.obj().mockReturnValueAt('foo', 'bar', nest.curry(3));

expect(mock).toHaveBeenNestedCalledWith(nest.args.foo('a', 'b').bar('c')('d', 'e')('f'));

Instead of:

const deeperNestedFunction = jest.fn();
const nestedFunction = jest.fn().mockReturnValue(deeperNestedFunction);
const nestedObject = { bar: jest.fn().mockReturnValue(nestedFunction) };
const mock = { foo: jest.fn().mockReturnValue(nestedObject) };

expect(mock).toHaveBeenCalledWith('a', 'b');
expect(nestedObject).toHaveBeenCalledWith('c');
expect(nestedFunction).toHaveBeenCalledWith('d', 'e');
expect(deeperNestedFunction).toHaveBeenCalledWith('f');

Installation

$ npm install jest-nest

Configuration

Create a setup file:

import { init } from 'jest-nest';

init();

And load it in your jest config:

import { Config } from 'jest';

const config: Config = {
  ...
  setupFilesAfterEnv: ['./test/setup.ts'],
};

export default config;

Usage

Curried functions

it('expects curried function call', () => {
  const mockImplementation = (a, b, c, d) => 'my return value';
  const curryFn = nest.curry(mockImplementation);

  const result = nestedFn('a', 'b')({ foo: 'bar' })('c');

  // Make any expectation against curryFn.uncurried like you would with any jest.Mock
  expect(curryFn.uncurried).toHaveBeenCalledWith('a', 'b', { foo: expect.any(String) }, 'c');
  // Or make expectations on how the mock was called
  expect(curryFn).toHaveBeenNestedCalledWith(nest.args('a', 'b')({ foo: expect.any(String) })('c'));

  expect(result).toBe('my return value');
});

or without an implementation

it('expects curried function call', () => {
  const arity = 4;
  const curryFn = nest.curry(arity);

  const result = nestedFn('a', 'b')({ foo: 'bar' })('c');

  expect(curryFn.uncurried).toHaveBeenCalledWith('a', 'b', { foo: expect.any(String) }, 'c');
});

or with a curried function as implementation

it('expects curried function call', () => {
  import myCurriedFunc from './myFunc';

  // Because the function is curried, the arity cannot be derived automatically
  const curryFn = nest.curry(myCurriedFunc, 4);

  const result = nestedFn('a', 'b')({ foo: 'bar' })('c');

  // Expectations can be made on full chains
  expect(curryFn.uncurried).toHaveBeenCalledWith('a', 'b', { foo: expect.any(String) }, 'c');
  // or make expectations on how the mock was (partially) called
  expect(curryFn).toHaveBeenNestedCalledWith(nest.args('a', 'b'));
});

Chained functions

For nested functions with a fixed depth of nesting and possibly with optional arguments, the nesting mock can be used.

it('expects nested function call', () => {
  const nestedFn = nest.fn(
    3, // depth, optional, default: 2
    () => 'my return value', // tail implementation, optional
  );

  const result = nestedFn('a', 'b')({ foo: 'bar' })('c');

  expect(nestedFn).toHaveBeenNestedCalledWith(nest.args('a', 'b')({ foo: expect.any(String) })('c'));
  expect(result).toBe('my return value');
});

(Nested) objects

The basic Object mock is an indexer of functions that return an object mock (i.e. you can call any string/symbol on the mock and it will return a new mock).

it('expects a nested object', () => {
  const mock = nest.obj();

  mock.foo('a').bar('b', 'c').baz('d');

  expect(mock).toHaveBeenNestedCalledWith(nest.args.foo('a').bar('b', 'c').baz('d'));
});

The Object mock can be configured to return given values at given paths:

it('sets values at paths' () => {
  const mock = nest
    .obj()
    .mockReturnValueAt('foo', 'bar', 42) // mock.foo(...).bar(...) returns 42
    .mockResolvedValueAt('foo', 'baz', 42) // mock.foo(...).bar(...) returns a resolved promise with value 42
    .mockRejectedValueAt('bar', 'foo', 'oops') // mock.bar(...).foo(...) returns a rejected promise with value 'oops'
    .mockGetValueAt('bar', 'baz', 42); // mock.bar(...).baz gets a property with value 42
});

or set a given implementation at a given path:

it('sets an implementation at a path', () => {
  const mock = nest
    .obj()
    .mockImplementationAt('isEven', (value: number) => value % 2 === 0) // mock.isEven(2) returns true since 2 is even
    .mockImplementationAt('adderOf', 'add', function (this: CallState, value: number) {
      const [adderOfArgs] = this.callPath; // Gets the arguments of the adderOf call
      const adderValue = adderOfArgs[1]; // Gets the first argument (argument at index 0 is the name of the property ('adderOf'))

      return adderValue + value;
    }); // mock.adderOf(5).add(2) returns 7
});

By default the object mock returns an object mock when calling a property for which no path has been set. This behaviour can be overridden:

it('sets the strictness of the object mock', () => {
  const mock = nest
    .obj() // mock.foo() returns an object mock
    .strict() // mock.foo returns 'undefined', since no return value has been set for path 'foo'
    .explicit() // alias for mock.strict()
    .implicit(); // mock.foo() returns an object mock
});

Combined mocks

Nest mocks, when combined, allow expectations over the entire chain:

it('supports expectations across multiple nest mocks', () => {
  const mock = nest.obj().mockReturnValueAt(
    'foo',
    'bar',
    nest.curry(() => nest.obj(), 4),
  );

  mock.foo('a').bar('b')('c')('d', 'e')('f').baz('g');

  expect(mock).toHaveBeenCalledTimes(1);
  expect(mock).toHaveBeenNestedCalledWith(nest.args.foo('a').bar('b')('c')('d', 'e')('f').baz('g'));
});

Api reference

Mocks

interface CallState {
      readonly callPath: ReadonlyArray<ReadonlyArray<any>>;
}

export type NestingMock = jest.Mock & CallState;

export type CurryMock = NestingMock & {
  uncurried: jest.Mock;
};

export type ObjectMock<Shape, Strict extends boolean> = NestingMock & {
  mockImplementationAt: (...path: string[], implementation: (this: CallState, ...args: any[]) => any): ObjectMock<NewShape, Strict>;
  mockReturnValueAt: (...path: string[], value: any) => any): ObjectMock<NewShape, Strict>;
  mockResolvedValueAt: (...path: string[], value: any): ObjectMock<NewShape, Strict>;
  mockRejectedValueAt: (...path: string[], value: any): ObjectMock<NewShape, Strict>;
  mockGetValueAt: (...path: string[], value: any): ObjectMock<NewShape, Strict>;
  mockStrict: (): ObjectMock<Shape, true>;
  mockImplicit: (): ObjectMock<Shape, false>;
} & Shape & Record<string | number | symbol, Strict extends true ? never : jest.Mock<ObjectMock<{}, Strict>>>

export declare function fnCurried(mockImplementation: (...args: any[]) => any, arity?: number): CurryMock;
export declare function fnCurried(arity: number): CurryMock;

export declare function fnNested(depth?: number, tailImplementation?: (...args: any[]) => any): NestingMock;

export declare function objNested(): ObjectMock<{}, false>;

Expectations

namespace jest {
  interface Matchers<R> {
    toHaveBeenNestedCalledWith(nestedArgs: any[][] | NestingArgs): R;
  }
}

export type NestingArgs = {
  (...args: any[]): NestingArgs;
  args: any[][];
} & Record<string | number | symbol, (...args: any[]) => NestingArgs>;

export declare const nestingArgs: NestingArgs;

Global exports

declare global {
  var nest: {
    fn: typeof fnNested;
    chain: fnNested;
    curry: typeof fnCurried;
    obj: typeof objNested;
    args: typeof nestingArgs;
  };
}

Version history

v2.2.3

  • Support jest version >=26.6.3

v2.2

  • Object mocks

v2.1

  • Option to override arity of nest.mock (needed for curried implementations)
  • Improved installation experience

v2.0

  • Curried jest mock
  • Nesting mock binding to the tail function, to provide access to the callPath

v1.0:

  • Nested jest mock
  • Nesting args helper
  • toHaveBeenNestedCalledWith jest custom matcher

License

MIT © Teun Mooij