WordPress PHP Development with TDD and Functional Programming

python3 scripts/init_plugin.py my-plugin-name --path ~/projects
cd ~/projects/my-plugin-name
composer install

# 1. Write failing test
# Edit tests/Unit/FeatureTest.php
composer test  # Should fail (RED)

# 2. Commit failing test
git add tests/Unit/FeatureTest.php
git commit -m "test(feature): add test for new behavior"

# 3. Write minimal code to pass
# Edit src/Module.php
composer test  # Should pass (GREEN)

# 4. Auto-fix coding standards
composer lint:fix

# 5. Commit working code
git add src/Module.php
git commit -m "feat(feature): implement new behavior"

# 6. Refactor if needed
# Edit src/Module.php
composer test  # Should still pass
composer lint:fix

# 7. Commit refactoring
git add src/Module.php
git commit -m "refactor(feature): improve implementation"

composer test              # Run all tests
composer test:coverage     # Generate coverage report
composer lint              # Check coding standards
composer lint:fix          # Auto-fix coding standards
composer lint:errors       # Show only errors, skip warnings

plugin-name/
├── plugin-name.php          # Main plugin file
├── composer.json            # Dependencies and scripts
├── phpcs.xml.dist           # Coding standards config
├── phpunit.xml.dist         # Testing configuration
├── .gitignore               # Git ignore rules
├── README.md                # Documentation
├── src/                     # Source code (PSR-4 autoloaded)
│   ├── Plugin.php           # Main plugin class
│   └── functions.php        # Pure helper functions
├── tests/                   # PHPUnit tests
│   ├── bootstrap.php        # Test setup
│   ├── Unit/                # Unit tests (pure functions)
│   └── Integration/         # Integration tests (WordPress hooks)
└── assets/                  # Frontend assets
    ├── css/
    ├── js/
    └── images/

view references/tdd_patterns.md

view references/functional_patterns.md

view references/git_workflow.md

// Pure - deterministic transformation
function sanitize_username( string $username ): string {
    return strtolower( trim( $username ) );
}

// Pure - data validation
function is_valid_email( string $email ): bool {
    return (bool) filter_var( $email, FILTER_VALIDATE_EMAIL );
}

// Impure - database access
function get_user_preferences( int $user_id ): array {
    return get_user_meta( $user_id, 'preferences', true );
}

// Impure - output
function render_template( string $template, array $data ): void {
    extract( $data );
    include $template;
}

public function test_sanitize_username_lowercase(): void {
    $result = sanitize_username( 'JohnDoe' );
    $this->assertEquals( 'johndoe', $result );
}

use Brain\Monkey\Functions;

public function test_saves_user_preference(): void {
    Functions\expect( 'update_user_meta' )
        ->once()
        ->with( 123, 'theme', 'dark' )
        ->andReturn( true );
    
    $result = save_user_preference( 123, 'theme', 'dark' );
    
    $this->assertTrue( $result );
}

<rule ref="WordPress.WP.I18n">
    <properties>
        <property name="text_domain" type="array">
            <element value="your-plugin-slug"/>
        </property>
    </properties>
</rule>

<rule ref="WordPress.NamingConventions.PrefixAllGlobals">
    <properties>
        <property name="prefixes" type="array">
            <element value="your_plugin_prefix"/>
        </property>
    </properties>
</rule>

composer lint:fix

python3 scripts/init_plugin.py my-plugin --path /path/to/directory

// Main plugin file
add_action( 'plugins_loaded', function() {
    Plugin::get_instance()->init();
} );

// Plugin class
class Plugin {
    private static ?Plugin $instance = null;
    
    public static function get_instance(): Plugin {
        if ( null === self::$instance ) {
            self::$instance = new self();
        }
        return self::$instance;
    }
    
    public function init(): void {
        $this->register_hooks();
    }
    
    private function register_hooks(): void {
        add_action( 'init', [ $this, 'on_init' ] );
        add_filter( 'the_content', [ $this, 'filter_content' ] );
    }
}

// Pure function - easy to test
function apply_custom_discount( float $price, float $rate ): float {
    return $price * ( 1 - $rate );
}

// WordPress filter using pure function
add_filter( 'product_price', function( $price ) {
    return apply_custom_discount( $price, 0.1 );
} );

// Test is simple
public function test_applies_discount(): void {
    $result = apply_custom_discount( 100.0, 0.1 );
    $this->assertEquals( 90.0, $result );
}

// Compose transformations
function process_user_input( string $input ): string {
    return pipe(
        fn( $s ) => trim( $s ),
        fn( $s ) => strtolower( $s ),
        fn( $s ) => sanitize_text_field( $s )
    )( $input );
}

// Helper for function composition
function pipe( ...$functions ) {
    return fn( $value ) => array_reduce(
        $functions,
        fn( $carry, $fn ) => $fn( $carry ),
        $value
    );
}

# Ensure dependencies installed
composer install

# Clear cache
rm -rf .phpunit.cache

# Run with verbose output
vendor/bin/phpunit --verbose

# Auto-fix most issues
composer lint:fix

# Check what can't be auto-fixed
composer lint:errors

# View detailed error
composer lint

protected function setUp(): void {
    parent::setUp();
    \Brain\Monkey\setUp();
}

protected function tearDown(): void {
    \Brain\Monkey\tearDown();
    parent::tearDown();
}