What is the difference between mocking and stubbing?

Question

Accepted Answer

**Mocking** — verify interactions. **Stubbing** — provide canned responses.

**Mocking:**
- Verify method calls.
- Check call count, arguments.
- Behavior verification.
- Framework: Jest mocks.

```
Mocking:
const mock = jest.fn();
userService.create(mock);
expect(mock).toHaveBeenCalledWith({name: "John"});
(Verify it was called)
```

**Stubbing:**
- Provide predetermined responses.
- Don't verify calls.
- State verification.
- Framework: Sinon stubs.

```
Stubbing:
jest.spyOn(db, "query").mockReturnValue([{id: 1}]);
const result = db.query("SELECT * FROM users");
expect(result).toEqual([{id: 1}]);
(Provide canned response)
```

**Key differences:**
- **Mock** — verify interactions.
- **Stub** — provide responses.
- **Mock** — behavior.
- **Stub** — state.

Systems Analyst: What is the difference between mocking and stubbing?