Write useful test matchers compatible with Jest and Jasmine.



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What A JavaScript library to write test Matchers compatible with all versions of Jest and Jasmine.
Why The way you write tests in Jasmine and Jest is extremely similar, but the APIs for adding custom matchers vary wildly between Jasmine 1.x, Jasmine 2.x, and Jest. This library aims to remove those obstacles and encourage Developers to share useful matchers they've created with the community.
How Developers use the API from this library, which converts them to be compatible with whichever test framework is running.


npm install --save-dev add-matchers


Include this library after your test framework but before your tests, and register your matchers before your tests as well.


The argument passed to expect is always the last argument passed to your Matcher, with any other arguments appearing before it in the order they were supplied. This means that, in the case of expect(recieved).toBeAwesome(arg1, arg2, arg3), your function will be called with fn(arg1, arg2, arg3, recieved).

Arguments are ordered in this way to support partial application and increase re-use of matchers.


If we wanted to use the following Matchers in our tests;

// matcher with 0 arguments

// matcher with 1 argument

// matcher with Many arguments
expect([100, 14, 15, 2]).toContainItems(2, 15, 100);

We would create them as follows;

var addMatchers = require('add-matchers');

  // matcher with 0 arguments
  toBeEvenNumber: function(received) {
    // received : 4
    return received % 2 === 0;
  // matcher with 1 argument
  toBeOfType: function(type, received) {
    // type     : 'Object'
    // received : {}
    return Object.prototype.toString.call(received) === '[object ' + type + ']';
  // matcher with many arguments
  toContainItems: function(arg1, arg2, arg3, received) {
    // arg1     : 2
    // arg2     : 15
    // arg3     : 100
    // received : [100, 14, 15, 2]
    return (
      received.indexOf(arg1) !== -1 &&
      received.indexOf(arg2) !== -1 &&
      received.indexOf(arg3) !== -1

For more examples, see Jasmine Matchers which is built using this library.

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