I want to test if an array is empty or contains objects of a certain structure. In pseudo code it could be something like this:

expect([])
  .toHaveLength(0)
  .or
  .arrayContaining(
    expect.toMatchObject(
     { foo: expect.any(String) }
    )
  ) => true

expect([{foo: 'bar'}])
  .toHaveLength(0)
  .or
  .arrayContaining(
    expect.toMatchObject(
     { foo: expect.any(String) }
    )
  ) => true

expect([1])
  .toHaveLength(0)
  .or
  .arrayContaining(
    expect.toMatchObject(
      { foo: expect.any(String) }
    )
  ) => false

Maybe I'm getting it wrong on the how things work in Jest, but to me my problem looks like an or-question.

I want to test if an array is empty or contains objects of a certain structure. In pseudo code it could be something like this:

expect([])
  .toHaveLength(0)
  .or
  .arrayContaining(
    expect.toMatchObject(
     { foo: expect.any(String) }
    )
  ) => true

expect([{foo: 'bar'}])
  .toHaveLength(0)
  .or
  .arrayContaining(
    expect.toMatchObject(
     { foo: expect.any(String) }
    )
  ) => true

expect([1])
  .toHaveLength(0)
  .or
  .arrayContaining(
    expect.toMatchObject(
      { foo: expect.any(String) }
    )
  ) => false

Maybe I'm getting it wrong on the how things work in Jest, but to me my problem looks like an or-question.

• javascript
• testing
• jestjs

1 Answer 1

The best way to encapsulate a logical or in your test suite would be to just exclude the particular case inside of the test itself. For example:

it('has an array of objects', () => {
  if (arr.length > 0) {
    expect(arr).toBe(expect.arrayContaining(expect.toMatchObject({ foo: expect.any(String) })));
  }
});

However, I think a more unit test-friendly approach would be to separate your concerns. One test for when there is an empty array, and one test for when the foo property is set to 'bar', etc.