Override functions

Every runtime-provided WordPress function is guarded by function_exists(). Define a function before WP_Runtime::boot() to prevent "Unitest WP Copy" from loading its implementation.

Full override

Define the replacement in the global namespace in your test bootstrap:

require_once dirname( __DIR__ ) . '/vendor/autoload.php';

function sanitize_locale_name( $locale_name ) {
	return 'test-locale';
}

\Unitest_WP_Copy\WP_Runtime::boot();
\WP_Mock::bootstrap();

When the runtime reaches its guarded declaration:

if ( ! function_exists( 'sanitize_locale_name' ) ) :
	// Runtime implementation.
endif;

the function already exists, so the runtime implementation is skipped. All code in the PHP process then calls your replacement.

When to use it

A full override is useful when:

• a copied function is not marked as mockable;
• the replacement should apply to the entire test process;
• a stable project-level test implementation is required.

Keep the replacement signature compatible with the WordPress function. Define it once in the suite bootstrap, not inside an individual test: PHP functions cannot be removed or redefined during the same process.

Full override versus WP_Mock

Use WP_Mock when the installed SYMBOLS-INFO.md marks a function as mockable and individual tests need different return values or expectations.

Use a full override when the original runtime function must never be loaded. Because the replacement is defined first, it also bypasses the runtime's WP_Mock-aware implementation.

Avoid overriding foundational functions unless the replacement preserves the behavior required by other copied functions. A process-wide override can affect every nested runtime call.