predicate.test.js

import each from 'jest-each';
import predicate from './predicate';

describe('toBeDate Predicate', () => {
  test('returns true when given a valid date', () => {
    expect(predicate(new Date('12/25/2017'))).toBe(true);
  });

  each([
    [new Date('01/90/2018')],
    [new Date('32/01/2018')],
    [true],
    [false],
    [''],
    [0],
    [{}],
    [() => {}],
    [undefined],
    [null],
    [NaN]
  ]).test('returns false when given: %s', given => {
    expect(predicate(given)).toBe(false);
  });
});