to be

• <any> [not] to be <any>

Asserts equality using Object.is/the SameValue algorithm.

const obj = {};
expect(obj, 'to be', obj);
expect(1, 'to be', 1);
expect(null, 'to be', null);
expect(undefined, 'to be', obj.foo);
expect(true, 'to be', !false);

The SameValue/Object.is algorithm has some subtle differences compared to the === operator, which makes it more suitable for an assertion lib:

expect(NaN, 'to be', NaN);
expect(-0, 'not to be', 0);

In case of a failing expectation you get the following output:

expect('1', 'to be', 1);

expected '1' to be 1

This assertion can be negated using the not flag:

expect({}, 'not to be', {});
expect(1, 'not to be', true);
expect('1', 'not to be', 1);
expect(null, 'not to be', undefined);
expect(0, 'not to be', 'null');
expect(undefined, 'not to be', 'null');
expect(false, 'not to be', 'true');
expect(true, 'not to be', 'false');

In case of a failing expectation you get the following output:

expect(1, 'not to be', 1);

expected 1 not to be 1