Mis on mock ja stub? Kuidas nad erinevad?

Mocks and stubs are types of test doubles used in unit testing to simulate the behavior of real dependencies of an object.

Stub:

• Provides "placeholder" behavior for a test scenario.
• Responds to method calls by returning predefined values.
• Does not verify interactions. Its purpose is to supply data to the tested object for further processing.

Mock:

• Similar to a stub but with added interaction verification logic.
• Contains expectations about which methods should be called, how many times, and with what arguments.
• The test checks not only the result but also the correctness of the interaction with the mock.

<?php
// Example of a mock object
use PHPUnit\Framework\TestCase;
use PHPUnit\Framework\MockObject\MockObject;

class UserServiceTest extends TestCase {
    public function testGetUserByIdCallsDatabase(): void {
        $databaseMock = $this->createMock(Database::class);
        $databaseMock->expects($this->once()) // Expect one call
                     ->method('getUserById')
                     ->with(1) // Expect argument 1
                     ->willReturn(['id' => 1, 'name' => 'Test User']); // Expected return value

        $userService = new UserService($databaseMock);
        $user = $userService->getUserById(1);

        // Verify result and interaction via mock
        $this->assertNotEmpty($user);
        $this->assertEquals('Test User', $user['name']);
    }
}

Differences in the table:

Characteristic	Stub	Mock
Purpose	Provide data for operation	Verify interaction and data
Verification	Does not verify interactions	Checks how the object interacts
Behavior logic	Simply returns values	Contains call expectations
Who performs assert	The tested object or client	The mock itself (via expectations)