php-testing

name	php-testing
description	Write PHP tests with PHPUnit — unit tests, mocking, data providers, assertions, test doubles, and TDD workflow. Use when writing tests for WooCommerce extensions or PHP projects.

PHP Testing with PHPUnit

Before writing code

Fetch live docs: Web-search site:phpunit.de documentation for the latest PHPUnit documentation. Check https://phpunit.de/ for current version and features.

PHPUnit Fundamentals

Test Class Structure

• Extend PHPUnit\Framework\TestCase (or WC_Unit_Test_Case for WooCommerce)
• Test methods prefixed with test or annotated with #[Test]
• setUp() — runs before each test
• tearDown() — runs after each test
• setUpBeforeClass() / tearDownAfterClass() — run once per class

Assertions

Core assertions:

• assertEquals( $expected, $actual ) — loose equality
• assertSame( $expected, $actual ) — strict identity
• assertTrue( $condition ) / assertFalse( $condition )
• assertNull( $value ) / assertNotNull( $value )
• assertCount( $expected, $array )
• assertContains( $needle, $haystack )
• assertInstanceOf( $class, $object )
• assertArrayHasKey( $key, $array )
• assertStringContainsString( $needle, $haystack )

Exception Testing

• $this->expectException( InvalidArgumentException::class )
• $this->expectExceptionMessage( 'Expected message' )
• $this->expectExceptionCode( 404 )

Test Doubles

Mocks

Create mock objects to verify interactions:

$mock = $this->createMock( PaymentProcessor::class );
$mock->expects( $this->once() )
     ->method( 'charge' )
     ->with( $this->equalTo( 29.99 ) )
     ->willReturn( true );

Stubs

Return predetermined values without verifying calls:

$stub = $this->createStub( PriceCalculator::class );
$stub->method( 'calculate' )->willReturn( 29.99 );

Expectation Methods

• $this->once() — called exactly once
• $this->exactly( $n ) — called exactly n times
• $this->never() — not called
• $this->atLeastOnce() — called one or more times
• $this->any() — any number of calls

willReturn Variants

• willReturn( $value ) — return fixed value
• willReturnMap( $map ) — return based on arguments
• willReturnCallback( $callable ) — custom logic
• willThrowException( $exception ) — throw on call

Data Providers

What They Do

Supply multiple test cases to a single test method:

public static function priceProvider(): array {
    return [
        'regular price' => [ 29.99, 29.99, '' ],
        'sale price'    => [ 29.99, 19.99, '19.99' ],
        'zero price'    => [ 0.00, 0.00, '' ],
    ];
}

#[DataProvider('priceProvider')]
public function test_get_display_price( float $regular, float $expected, string $sale ): void {
    // test with each data set
}

Best Practices for Providers

• Name data sets descriptively (keyed array)
• Keep providers as static methods
• Return arrays of arrays (each inner array = one test case)
• Use #[DataProvider('methodName')] attribute

WordPress/WooCommerce Testing Specifics

WP_UnitTestCase

• Provides WordPress-loaded environment
• Each test wrapped in a database transaction (auto-rollback)
• Factory methods: $this->factory->post, $this->factory->user
• go_to( $url ) — simulate page load
• set_current_screen( 'edit-post' ) — simulate admin screen

Mocking WordPress Functions

Use WP_Mock or Brain\Monkey libraries:

• Mock add_action, add_filter, do_action, apply_filters
• Mock wp_remote_get, get_option, etc.
• Useful for isolated unit tests without WordPress bootstrap

Mocking HTTP Requests

Filter pre_http_request to intercept wp_remote_get() / wp_remote_post():

add_filter( 'pre_http_request', function( $preempt, $args, $url ) {
    return [ 'response' => [ 'code' => 200 ], 'body' => '{"status":"ok"}' ];
}, 10, 3 );

Test Organization

Directory Structure

tests/
├── bootstrap.php           # Test bootstrap
├── Unit/                   # Pure unit tests (no WP)
│   └── PriceCalculatorTest.php
├── Integration/            # Tests with WP/WC loaded
│   ├── ProductTest.php
│   └── OrderTest.php
└── E2E/                    # Playwright end-to-end
    └── specs/

phpunit.xml.dist Configuration

• Define test suites: unit, integration
• Set bootstrap file
• Configure coverage report output
• Set environment variables

TDD Workflow

1. Red — write a failing test that describes the desired behavior
2. Green — write the minimum code to make the test pass
3. Refactor — clean up code while keeping tests green
4. Repeat

Best Practices

• One assertion per test (when practical)
• Name tests descriptively: test_process_payment_returns_success_for_valid_card
• Use data providers for parameterized tests
• Mock external dependencies (APIs, databases, file system)
• Test edge cases: null values, empty strings, boundary values, invalid input
• Keep unit tests fast — no network, no filesystem, no database
• Use integration tests for WordPress/WooCommerce interaction testing
• Run tests in CI on every push

Fetch the PHPUnit documentation for exact assertion signatures, mock API, and configuration options before implementing.