expect(map).to.be.empty does not behave naturally

[janakdr]

it('expect map', () => {
    expect(new Map([['a', 1]])).to.not.be.empty;
});

This test fails with the incorrect assertion: "expected {} not to be empty". It seems like Cypress is interpreting the Map object as some kind of DOM element, which it thinks is empty? Similarly, this test incorrectly passes if the .not is removed.

Cypress doesn't explicitly say what it does for the .empty predicate in its assertions documentation but it does link to the full list of assertions which specify that for a Map, it will assert that the map has size 0. Even if the test code is changed to expect(new Map([['a', 1]])).to.be.a('map').that.is.not.empty the "empty" assertion is the one that fails.

[jennifer-shehane]

This comes directly from Chai assertions and was not supported until Chai 4.0 as noted here: chaijs/chai#781

Support for asserting empty against Map will come in Cypress v4.0 which includes an update of Chai to 4.2.0 and other breaking changes. #4270

The code for this is done in #4270, but this has yet to be released. We'll update this issue and reference the changelog when it's released.

[flotwig]

Released in 4.0.0.