PHPUnit Testing 🧪

Write unit tests, use test doubles (mocks, stubs, fakes), and test-drive your PHP code with PHPUnit for rock-solid applications.

What You'll Learn in This Lesson

• Write unit tests with assertions and expected exceptions
• Use stubs, mocks, fakes, and spies for dependencies
• Test a real registration service with isolated components
• Understand the test pyramid: unit vs integration vs E2E
• Run tests and interpret results

Note: PHP runs on a server. Our examples simulate PHP logic using JavaScript. To run real PHP, install PHP.

🎯 Real-World Analogy: Tests are like a safety net for trapeze artists. You can perform daring refactors (flips) knowing that if something goes wrong, the tests (net) will catch it. Mocks are like practice dummies — you test your routine without needing a real partner (database, email service).

Unit Testing Fundamentals

A unit test verifies a single function or class in isolation. Each test follows the Arrange-Act-Assert pattern: set up inputs, call the function, verify the output. Good tests are fast, independent, and deterministic — they always produce the same result.

Try It: Unit Test Suite

Test a Calculator and ShoppingCart with assertions and exception handling

Try it Yourself »

JavaScript

// Unit Testing with PHPUnit
console.log("=== Why Write Tests? ===");
console.log();
console.log("  Without tests: 'I think it works' (until production breaks)");
console.log("  With tests:    'I know it works' (tests prove it)");
console.log();
console.log("  Test types:");
console.log("  • Unit tests     — Test a single function/class in isolation");
console.log("  • Integration    — Test multiple components together");
console.log("  • Feature/E2E   — Test full HTTP request/response cycle");

...

Mocks, Stubs & Fakes

Real dependencies (databases, email services, APIs) make tests slow and unreliable. Replace them with test doubles: stubs return pre-set values, fakes provide working in-memory implementations, and mocks verify that methods were called with the correct arguments.

Try It: Test Doubles

Test user registration with fake repositories and stub email services

Try it Yourself »

JavaScript

// Test Doubles: Mocks, Stubs, and Fakes
console.log("=== Test Doubles Explained ===");
console.log();
console.log("  Stub:  Returns pre-configured answers. Doesn't verify calls.");
console.log("  Mock:  Verifies that specific methods were called correctly.");
console.log("  Fake:  Working implementation (e.g., in-memory database).");
console.log("  Spy:   Records calls for later inspection.");
console.log();

// Demonstrate test doubles
class EmailServiceStub {
  constructor() { this.sent = [];
...

⚠️ Common Mistakes

⚠️

Testing implementation, not behavior — Don't test that a specific private method was called. Test that the public output is correct. Refactoring shouldn't break tests.

⚠️

Tests that depend on each other — Each test must create its own state. Never rely on another test running first or leaving data behind.

💡

Pro Tip: Aim for the test pyramid: many unit tests (fast), some integration tests (medium), few E2E tests (slow). Run unit tests on every commit, integration tests in CI.

📋 Quick Reference — PHPUnit

Concept	Description
assertEquals()	Assert two values are equal
expectException()	Assert a specific exception is thrown
createMock()	Create a mock object for a class
setUp()	Runs before each test method
@dataProvider	Run same test with different inputs

🎉 Lesson Complete!

You can now write professional tests! Next, learn to build and publish reusable Composer packages.