const expect = require('expect');
const {isNull} = require('./_30s.js');

test('isNull is a Function', () => {
  expect(isNull).toBeInstanceOf(Function);
});
test('passed argument is a null', () => {
  expect(isNull(null)).toBeTruthy();
});
test('passed argument is a null', () => {
  expect(isNull(NaN)).toBeFalsy();
});