Chai assertion error when comparing arrays

Question

I have encountered a weird error when trying to assert that a result should equal to an array, when using Chai.

Code Example

   describe("compare array", function() {
        it("should return an empty array", function() {
            const result = getEmptyList(); // just a silly example
            expect(result).to.equal([]);
        });
   });

Result

  × compare array
    PhantomJS 2.1.1 (Windows 8.0.0)
  expected [ find: [Function] ] to equal [ find: [Function] ]
  AssertionError@C:/Code/example/node_modules/chai/chai.js:9449:24
  assert@C:/Code/example/node_modules/chai/chai.js:239:31
  assertEqual@C:/Code/example/node_modules/chai/chai.js:1387:18
  methodWrapper@C:/Code/example/node_modules/chai/chai.js:7824:30
  test/unit/utils/example.js:5:32

When I instead expect the length of the result to equal zero, it works fine. Can anyone share some insights to why this is happening. Why is [ find: [Function] ] all of a sudden expected, instead of [] as was desired?

I am using Karma as my test runner.

score 4 · Accepted Answer · answered Oct 31 '19 at 10:34

4

Since one array is never === to another, for arrays you need the deep qualifier for equals:

expect(result).to.deep.equal([]);
// --------------^^^^^

From the docs:

Causes all .equal, .include, .members, .keys, and .property assertions that follow in the chain to use deep equality instead of strict (===) equality.

answered Oct 31 '19 at 10:34

T.J. Crowder

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1

Thanks TJ, you made my day! – ProgrammerPer Oct 31 '19 at 10:39
1

@ProgrammerPer - Glad to help! I belatedly realized that it had to be a duplicate, and found the canonical for it. – T.J. Crowder Oct 31 '19 at 10:59
Great, no worries! – ProgrammerPer Oct 31 '19 at 12:34

Chai assertion error when comparing arrays

1 Answers1