What are the test matchers in Jest? How to use custom matchers?

Jest provides various test matchers to verify different conditions:

Equality Matchers:

• toBe(value): Strict equality (===)
• toEqual(value): Deep equality
• toStrictEqual(value): Strict deep equality (including undefined properties)
• toMatchObject(object): Partial object matching

Truthiness Matchers:

• toBeNull(): Matches only null
• toBeUndefined(): Matches only undefined
• toBeDefined(): Not undefined
• toBeTruthy(): Truthy values
• 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 or substring

Array Matchers:

• toContain(item): Contains element
• toContainEqual(item): Contains equal element
• toHaveLength(number): Array length
• toBeArray(): Is an array

Object Matchers:

• toHaveProperty(keyPath, value): Has specific property
• toMatchObject(object): Partial object matching

Function Matchers:

• toHaveBeenCalled(): Was called
• toHaveBeenCalledWith(...args): Called with specific arguments
• toHaveBeenCalledTimes(n): Number of calls
• toHaveReturned(): Has return value
• toHaveReturnedWith(value): Returned specific value

Exception Matchers:

• toThrow(error?): Throws error
• toThrowErrorMatchingSnapshot(): Error snapshot

Custom Matchers:

javascript
expect.extend({
  toBeWithinRange(received, floor, ceiling) {
    const pass = received >= floor && received <= ceiling;
    return {
      pass,
      message: () => pass
        ? `expected ${received} not to be within range ${floor}-${ceiling}`
        : `expected ${received} to be within range ${floor}-${ceiling}`
    };
  }
});

test('number within range', () => {
  expect(100).toBeWithinRange(90, 110);
});

Negation Matchers: All matchers can be negated using .not:

javascript
expect(value).not.toBe(42);
expect(array).not.toContain('item');