Matchers

Jest · Reference cheat sheet

📋 Overview

expect(value) matchers assert equality, truthiness, numbers, strings, collections, and errors. Prefer asymmetric matchers for partial object checks.

🔧 Core concepts

Matcher	Use
`toBe`	Referential / primitives (`Object.is`)
`toEqual`	Deep equality
`toStrictEqual`	Deep + undefined keys
`toMatch` / `toContain`	String / array
`toThrow`	Sync exceptions
`toBeCloseTo`	Floats
`toHaveBeenCalled`	Mocks

Chain .not, .resolves, .rejects.

💡 Examples

Equality:

expect(1 + 1).toBe(2);
expect({ a: 1 }).toEqual({ a: 1 });
expect({ a: 1 }).toStrictEqual({ a: 1 });

Truthiness & numbers:

expect(x).toBeTruthy();
expect(x).toBeNull();
expect(x).toBeUndefined();
expect(0.1 + 0.2).toBeCloseTo(0.3);
expect(score).toBeGreaterThan(10);

Collections & strings:

expect(['a', 'b']).toContain('a');
expect('hello').toMatch(/ell/);
expect({ a: 1, b: 2 }).toMatchObject({ a: 1 });
expect([{ id: 1 }]).toContainEqual({ id: 1 });

Asymmetric:

expect(user).toEqual({
  id: expect.any(Number),
  email: expect.stringMatching(/@/),
  meta: expect.objectContaining({ role: 'admin' }),
});

Errors:

expect(() => parse('')).toThrow(Error);
expect(() => parse('')).toThrow(/empty/);

⚠️ Pitfalls

toBe on objects compares references — use toEqual.
Floating point with toBe — use toBeCloseTo.
toThrow needs a wrapped function, not a thrown call.
Over-specific snapshots instead of focused matchers.
Forgetting await expect(...).resolves for promises.

Matchers

Matchers

📋 Overview

🔧 Core concepts

💡 Examples

⚠️ Pitfalls

🔗 Related

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