Throw
toThrow
executes a function passed in expect, and verifies that it throws an error.
In this case, you're not passing expect a function. You're executing a function that throws an error. toThrow is never executed, and even if it were, it would throw an error, telling you that it should receive a function, but received something else instead.
expect(someFunctionThatThrows())
is essentially the same as expect(throw new Error())
.