expect.any(constructor)

expect.any(constructor) matches anything that was created with the given constructor. You can use it inside toEqual or toBeCalledWith instead of a literal value. For example, if you want to check that a mock function is called with a number:

function randocall(fn) {
  return fn(Math.floor(Math.random() * 6 + 1));
}
test('randocall calls its callback with a number', () => {
  const mock = jest.fn();
  randocall(mock);
  expect(mock).toBeCalledWith(expect.any(Number));
});