使用mocha和chai测试作为数组的输出

Question

I'm new to testing Javascript, so this may be entirely obvious. I'm using the framework Mocha and the assertion library Chai to test a Javascript tool.

I have several functions which output an array with several elements. How does one use Chai to test this?

Here is an example:

var chai = require('chai');
var assert = chai.assert;
var expect = chai.expect;

// define an array
var Arr = [3, 4, 5, 6, 10];

console.log(Arr.slice(1, 3))
// outputs [4, 5]

// this will fail
describe('subsetting an array', function() {
  it('array subset', function() {
    assert.equal(Arr.slice(1, 3), [4, 5])
  });
});

So this test fails with the following error:

AssertionError: expected [ 4, 5 ] to equal [ 4, 5 ]

(1) Why does assert.equal() fail? These are both data structures of type "Array"

(2) How should one correctly test this with Chai?

Answer 1

assert.equal() tests comparison using == , and given that slice() creates a new array, although both have the same number of elements, they are not the same element (they are actually two different arrays, containing the same integers)

I think you should use eql method

// Target array is deeply (but not strictly) equal to [1, 2]
expect([1, 2]).to.eql([1, 2]).but.not.equal([1, 2]);

See that there's a difference between eql and equal

If you want to stick to asssert, I think (I don't have the console here to test it) that you can use deepEqual

assert.deepEqual({ tea: 'green' }, { tea: 'green' });

Not quite sure if it works for arrays, though

Answer 2

I think you need to check for deep equality using .deepEqual

http://www.chaijs.com/api/assert/#method_deepequal