Phpunit Testing

By the end of this lesson you'll install PHPUnit with Composer and write real automated tests — assertions, data providers, setup/teardown, and mocks — so you can refactor and ship PHP with confidence instead of crossing your fingers.

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Part of the free Php course at LearnCodingFast — hands-on lessons with examples you run in your browser, plus practice exercises and a quick quiz.

What You'll Learn in This Lesson

1️⃣ Installing PHPUnit with Composer

PHPUnit is the standard testing framework for PHP — a tool that runs your tests and tells you which passed and which failed. You install it with Composer (PHP's package manager) as a dev dependency , meaning it's available while you build but never shipped to your live server. After installing, Composer places a runnable program at vendor/bin/phpunit .

One tiny config file tells the runner where your tests live, so you can just type ./vendor/bin/phpunit with no arguments. By convention, source code goes in src/ and tests go in tests/ .

2️⃣ Your First TestCase

A test is just a class that extends TestCase , with one or more public methods whose names start with test . Inside each method you follow Arrange-Act-Assert : build what you need, call the one thing you're testing, then check the result with an assertion . An assertion is a line that says "this had better be true" — if it isn't, the test fails. To check that code throws , you call expectException() before the line that should throw.

Read the output bottom-up: OK (2 tests, 2 assertions) means both methods ran and every assertion held. Each dot in .. is one passing test; a failure shows as F , an error as E .

3️⃣ The Assertions You'll Use Most

PHPUnit ships dozens of assertions, but a handful cover nearly everything. The key distinction is assertEquals versus assertSame : assertEquals compares values loosely (so 5 equals "5" ), while assertSame compares value and type strictly (like === ). Reach for assertSame by default — it catches accidental string-vs-int bugs. The exception is floats, where rounding means you use assertEqualsWithDelta .

4️⃣ setUp() and tearDown(): Fresh State Every Test

Tests must be isolated — each one runs as if it were the only test in the world. PHPUnit helps by calling setUp() before every test method , so you can build a fresh object there instead of repeating yourself. The matching tearDown() runs after every test to undo side effects (delete temp files, roll back a database). Because setUp() re-runs each time, no test can leak state into the next.

Now you try. The test class below is almost complete — fill in each ___ with the right assertion name using the 👉 hint, then run it and check it against the Output panel.

5️⃣ Data Providers: One Test, Many Inputs

When you want to test the same logic against lots of inputs — valid and invalid emails, edge-case numbers — don't copy-paste the test. A data provider is a static method that returns an array of rows ; each row is the arguments for one run. You attach it with the #[DataProvider('methodName')] attribute, and PHPUnit runs the test once per row , reporting each as its own pass or fail. Adding a new case becomes a one-line change.

Your turn again. Below, a plain test needs to become data-driven. Fill in the expected numbers and the missing attribute name.

6️⃣ Mocking: Faking the Database and the Mailer

Real dependencies — a database, an email server, a payment API — make tests slow, flaky, and dangerous (you don't want a test emailing real users). The fix is a test double : a stand-in object. A stub just returns canned values so your code has something to work with. A mock goes further and verifies interactions — that a method was called the right number of times with the right arguments. PHPUnit's createMock() builds one from a class or interface; expects($this->once()) asserts it's called exactly once.

Notice the second test uses expects($this->never()) to prove a negative : a duplicate signup must not send a welcome email. That's behaviour you simply can't check by inspecting a return value — only a mock can assert it.

7️⃣ Running the Suite and Reading a Failure

You run everything with ./vendor/bin/phpunit tests/ . While debugging, narrow it down: ./vendor/bin/phpunit tests/CalculatorTest.php runs one file, and --filter testAddsTwoNumbers runs one method. When a test fails, PHPUnit prints the class, the method, what it expected vs what it got , and the exact file and line — read it carefully before touching code.

📋 Quick Reference — PHPUnit

No test code is filled in this time — just the class under test, a brief, and an outline. Write the test class yourself, run it with ./vendor/bin/phpunit , then check your result against the expected output in the comments. This is exactly the write-run-check loop you'll use on every real project.

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