Add ability to mock global functions

[aenglander]

When writing plugins/modules for legacy platforms like WordPress, Drupal < 8, or OS Commerce, it would be nice to be able to test the code. Unfortunately, they all use global functions and specify that if you want to test your code, write some sort of facade in front of the globals to mock. It would be much nicer to be able just mock the functions themselves as long as they do not exist. An example might be:

$get_user_metadata_mock = Phake::mockFunction('get_user_metadata');
Phake::when($get_user_metadata_mock)->call(Phake::anything())->thenReturn(array());

get_user_metadata(12345);

Phake::verify($get_user_metadata_mock)->call(12345);

[mollierobbert]

If your code is namespaced, mocking out function calls is quite easy with standard PHPUnit by redefining the functions inside the namespace.

See also: http://marcelog.github.io/articles/php_mock_global_functions_for_unit_tests_with_phpunit.html