In PHPUnit, you can mock global functions by namespace overlay, PHP Test Helpers extension, or encapsulating global functions as classes. 1. Use namespace: Rewrite the function under the same namespace as the code under test, which is only suitable for non-global calls; 2. Use PHP Test Helpers extension: Replace any global function through override_function(), but need to modify the php.ini configuration; 3. Encapsulate it as a class and dependency injection: encapsulate the global function into the class and use it through dependency injection. This class can be directly mocked during testing. This method is easier to maintain and comply with design principles.

In PHPUnit test, if you want to mock a global PHP function (such as time() , rand() , or global functions you define yourself), you will find that PHPUnit itself does not directly support this function. Because PHP design does not allow direct replacement of global functions. But there are some tricks you can do this.

Use namespace to override global functions

This is one of the most common and officially recommended practices. PHP allows you to "rewrite" functions in a specific namespace, and PHPUnit can mock certain functions using this.

Specific practices:

• Declare a namespace at the top of your test file that is the same as the code being tested.
• Then redefine the function you want to mock under this namespace.

 // Suppose the class you want to test is located in the App\Utils namespace App\Utils {
    // Here we mock time() function time() {
        return 1234567890; // Fixed return a timestamp}
}

This way, all calls in this namespace will use the version you defined, rather than the native time() .

Note: This method is only suitable for cases where the code under test uses the namespace, and can only mock functions that are not called through global or \time() .

Extensions with PHP Test Helpers

If the project is complicated or you need to mock many global functions, it is recommended to use the PHP Test Helpers extension.

It provides a tool called override_function() that can be used to replace any global function.

Installation method:

 pecl install test_helpers

Then add in php.ini :

 extension=test_helpers.so

Example of usage:

 override_function('time', '', 'return 1234567890;');

In this way, no matter which namespace calls time() , it will get the value you set.

The disadvantage is that the server configuration needs to be modified and cannot be enabled in all environments (for example, production environments or CI/CD do not have this extension by default).

Use a wrapper class or function instead of calling global functions directly

From the perspective of architectural design, relying on global functions will make the code difficult to test and maintain. Therefore, the more recommended approach is:

• Encapsulate global functions into a class.
• Dependency injection of this class in business code.
• You can directly mock this class during testing.

For example:

 class TimeService {
    public function getCurrentTime(): int {
        return time();
    }
}

Then use $timeService->getCurrentTime() in the business logic instead of calling time() directly. This allows you to easily replace it with a fixed value during testing.

advantage:

• Easier to test
• Improve code maintainability
• Follow the dependency injection principle

In general, the mock global PHP function is indeed a bit trampled in PHPUnit, but it is not impossible to solve. Priority is given to encapsulating functions as objects, secondly, using namespace to overwrite functions, and finally using extension tools. Basically, these methods are not complicated but they are easy to ignore details.

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