What are the common assertion methods in Jest? How to use expect and matchers?

Jest provides rich assertion methods, primarily used through the expect() function combined with matchers:

Common Matchers:

Equality Matchers:

• toBe(value): Strict equality (using ===)
• toEqual(value): Deep equality (recursively compares objects and arrays)
• toMatchObject(object): Partial object property matching
• toStrictEqual(value): Strict deep equality (including undefined properties)

Truthiness Matchers:

• toBeNull(): Matches only null
• toBeUndefined(): Matches only undefined
• toBeDefined(): Not undefined
• toBeTruthy(): Truthy values (not false, 0, "", null, undefined, NaN)
• toBeFalsy(): Falsy values

Number Matchers:

• toBeGreaterThan(number): Greater than
• toBeGreaterThanOrEqual(number): Greater than or equal
• toBeLessThan(number): Less than
• toBeLessThanOrEqual(number): Less than or equal
• toBeCloseTo(number, precision): Floating point approximate equality

String Matchers:

• toMatch(regexp | string): Matches regex or string
• toContain(item): Contains element

Async Matchers:

• resolves: Promise resolves
• rejects: Promise rejects

Examples:

javascript
expect(2 + 2).toBe(4);
expect({ name: 'John' }).toEqual({ name: 'John' });
expect(null).toBeNull();
expect(10).toBeGreaterThan(5);
expect('hello').toMatch(/ell/);