These assertions are the odd ducks. We don't have the mental stamina to categorize them properly.
Aliases:
to be truthy,to exist,to be ok
Success:
expect(1, 'to be truthy');
expect('hello', 'to be truthy');
expect(true, 'to exist');
expect({}, 'to be ok');
expect([], 'to exist');
Failure:
expect(0, 'to be truthy');
// AssertionError: Expected 0 to be truthy
expect('', 'to exist');
expect(false, 'to be ok');
expect(null, 'to exist');
expect(undefined, 'to be truthy');
Negation:
expect(0, 'not to be truthy');
expect('', 'not to exist');
expect(false, 'not to be ok');
Success:
expect(0, 'to be falsy');
expect('', 'to be falsy');
expect(false, 'to be falsy');
expect(null, 'to be falsy');
expect(undefined, 'to be falsy');
expect(NaN, 'to be falsy');
Failure:
expect(1, 'to be falsy');
// AssertionError: Expected 1 to be falsy
expect('hello', 'to be falsy');
expect(true, 'to be falsy');
Negation:
expect(1, 'not to be falsy');
expect('hello', 'not to be falsy');
expect(true, 'not to be falsy');
Success:
expect(0, 'to be defined');
expect('', 'to be defined');
expect(false, 'to be defined');
expect(null, 'to be defined');
Failure:
expect(undefined, 'to be defined');
// AssertionError: Expected undefined to be defined
Negation:
expect(undefined, 'not to be defined');