javascript - Testing anonymous function equality with Jest

Question

Is there a way to test anonymous function equality with jest@20?

I am trying to pass a test similar to:

const foo = i => j => {return i*j}
const bar = () => {baz:foo(2), boz:1}

describe('Test anonymous function equality',()=>{

    it('+++ foo', () => {
        const obj = foo(2)
        expect(obj).toBe(foo(2))
    });

    it('+++ bar', () => {
        const obj = bar()
        expect(obj).toEqual({baz:foo(2), boz:1})
    });    
});

which currently yields:

  ● >>>Test anonymous function equality ? +++ foo

    expect(received).toBe(expected)

    Expected value to be (using ===):
      [Function anonymous]
    Received:
      [Function anonymous]

    Difference:

    Compared values have no visual difference.

  ● >>>Test anonymous function equality ? +++ bar

    expect(received).toBe(expected)

    Expected value to be (using ===):
      {baz: [Function anonymous], boz:1}
    Received:
      {baz: [Function anonymous], boz:1}

    Difference:

    Compared values have no visual difference.

question from:https://stackoverflow.com/questions/45644098/testing-anonymous-function-equality-with-jest

Answer 1

In such situation, without rewriting your logic to use named functions, you don't really have another choice other than declaring the function before the test, e.g.

const foo = i => j => i * j
const foo2 = foo(2)
const bar = () => ({ baz: foo2, boz: 1 })

describe('Test anonymous function equality', () => {
  it('+++ bar', () => {
    const obj = bar()
    expect(obj).toEqual({ baz: foo2, boz: 1 })
  });    
});

Alternatively, you can check whether obj.bar is any function, using expect.any(Function):

expect(obj).toEqual({ baz: expect.any(Function), boz: 1 })

which might actually make more sense depending on the context of the test.