mock

bespin mock

A mocking library.

Install

$ npm install -D @testingrequired/bespin-mock

Usage

mockFunction

Setup mock function's return value based on call arguments. Verify mock functions were called with expected arguments.

import { mockFunction } from '@testingrequired/bespin-mock';

function getName() {
  return 'World';
}

function greeting(
  getNameFn: typeof getName /* The mock will pass this type check */
) {
  const name = getNameFn();
  console.log(`Hello, ${name}!`);
}

const mockGetName = mockFunction(getName);

// Mock setups are based on the calling arguments.
mockGetName.mock.whenCalledWithThenReturn([], 'Universe');

greeting(mockGetName); // Hello, Universe!

mockObject

Create a mocked instance of a class. All methods are mocked.

import { mockObject } from '@testingrequired/bespin-mock';

class Service {
  getNames(): Array<string> {
    return [];
  }
}

const mockService = mockObject(Service);

mockService.getNames.mock.whenCalledWithThenReturns([], ['foo', 'bar']);

mockSerivce.getNames(); // ['foo', 'bar']

Mock

The mock contains setups which match calling arguments to behaviors (e.g. returning values, throwing errors, doing nothing), methods for verifying calls, raw access to call and return sequences.

Setups

Mocks are strict by nature. Meaning they will throw an exception if a call is made without a matching setup. This is not configurable at this time.

whenCalledWithThenReturn

When called with args [a, b, c...] then return a "value".

import { mockFunction } from '@testingrequired/bespin-mock';

function numberToString(n: number): string {
  return n.toString(10);
}

const mockFn = mockFunction(numberToString);

mockFn.mock.whenCalledWithThenReturn([10], '100');

mockFn(10); // 100

whenCalledWithThenThrow

When called with args [a, b, c...] then throw error.

import { mockFunction } from '@testingrequired/bespin-mock';

function numberToString(n: number): string {
  return n.toString(10);
}

const mockFn = mockFunction(numberToString);

mockFn.mock.whenCalledWithThenThrow([10], new Error('Expected error message'));

mockFn(10); // Throws 'Expected error message'

whenCalledWithJustRun

When called with args [a, b, c...] then do nothing.

import { mockFunction } from '@testingrequired/bespin-mock';

function numberToString(n: number) {
  console.log(n);
}

const mockFn = mockFunction(numberToString);

mockFn.mock.whenCalledWithJustRun([10]);

mockFn(10); // Does nothing

reset

Mock setups can be emptied

import { mockFunction } from '@testingrequired/bespin-mock';

function numberToString(n: number) {
  console.log(n);
}

const mockFn = mockFunction(numberToString);

mockFn.mock.whenCalledWithJustRun([10]);

mockFn(10); // Does nothing

mockFn.mock.reset();

mockFn(10); // Throws because there are no matching setups

Verifying

verify

Verifies mock was called with expected arguments.

import { mockFunction } from '@testingrequired/bespin-mock';

function numberToString(n: number) {
  console.log(n);
}

const mockFn = mockFunction(numberToString);

mockFn.mock.whenCalledWithJustRun([10]);

mockFn(10); // Does nothing

mockFn.mock.verify([10]);

mockFn.mock.verify([20]); // Throws because no calls were made passing 20

verifyAll

Verify all setups were called.

import { mockFunction } from '@testingrequired/bespin-mock';

function numberToString(n: number) {
  console.log(n);
}

const mockFn = mockFunction(numberToString);

mockFn.mock.whenCalledWithJustRun([10]);

mockFn.mock.verifyAll(); // Throws because no calls were made passing 10

Recorded Data

Mocks record their input arguments and return values.

import { mockFunction } from '@testingrequired/bespin-mock';

function numberToString(n: number) {
  console.log(n);
}

const mockFn = mockFunction(numberToString);

mockFn.mock.whenCalledWithJustRun([10]);

mockFn(10);
mockFn(10);
mockFn(10);

mockFn.mock.calls; // [[10], [10], [10]]
mockFn.mock.returns; // [undefined, undefined, undefined]

clear

This recorded data can be cleared

import { mockFunction } from '@testingrequired/bespin-mock';

function numberToString(n: number) {
  console.log(n);
}

const mockFn = mockFunction(numberToString);

mockFn.mock.whenCalledWithJustRun([10]);

mockFn(10);
mockFn(10);
mockFn(10);

mockFn.mock.calls; // [[10], [10], [10]]
mockFn.mock.returns; // [undefined, undefined, undefined]

mockFn.mock.clear();

mockFn.mock.calls; // []
mockFn.mock.returns; // []