Jest Basics

Basic test
describe("Test Suite", () => {
  test("test case", () => {
    expect(2 + 2).toBe(4);
  });
});

Alternative syntax
it("should work", () => {
  expect(true).toBeTruthy();
});

Equality
expect(value).toBe(4);
expect(obj).toEqual({ a: 1 });

Truthiness
expect(value).toBeTruthy();
expect(value).toBeFalsy();
expect(value).toBeNull();
expect(value).toBeUndefined();

Numbers
expect(value).toBeGreaterThan(3);
expect(value).toBeLessThan(5);
expect(value).toBeCloseTo(0.3);

Arrays
expect(arr).toContain("item");
expect(arr).toHaveLength(3);

Strings
expect(str).toMatch(/pattern/);
expect(str).toContain("substring");

Objects
expect(obj).toHaveProperty("key");
expect(obj).toMatchObject({ a: 1 });

Run all tests
npx jest

Watch mode
npx jest --watch

Coverage
npx jest --coverage

Specific file
npx jest mytest.test.js

Update snapshots
npx jest -u