Skip to main content

Tests with Jest

Overview​

Basic test​

describe("scope of my test", () => {
  test("my test", () => expect(2).toBe(2));
});

Hooks​

describe("hooks", () => {
  before(() => {
    /* runs once before the first test in this block */
  });

  after(() => {
    /* runs once after the last test in this block */
  });

  beforeEach(() => {
    /* runs before each test in this block */
  });

  afterEach(() => {
    /* runs after each test in this block */
  });

  // test cases
});

Inclusive/Exclusive tests​

  • .only allows to run only the specified suite or test-case
  • .skip skip the specified suite or test-case
describe.only("inclusive", () => {
  /* ... */
});
// skip test
describe.skip("exclusive", () => {
  /* ... */
});

NOTE:

  • only and skip also work with the directive it

Expect​

Expect decorators​

  • .not negates the current assertion
  • .resolves unwrap the value of a fulfilled promise
  • .rejects unwrap the value of a failed promise

example:

expect(value).not.toBe(value);

Most common​

expect(value)
  .toBe(value)
  .toEqual(value)
  .toBeFalsy()
  .toBeTruthy()
  .toBeDefined();

Numbers​

expect(value)
  .toBeCloseTo(number, numDigits)
  .toBeGreaterThan(number)
  .toBeGreaterThanOrEqual(number)
  .toBeLessThan(number)
  .toBeLessThanOrEqual(number);

Objects​

expect(value)
  .toHaveProperty(keyPath, value)
  .toEqual(value); // true if props/values are similare

Errors​

expect(value).toThrow(error);