_n() function mocker always returns first string (singular)

[Jignesh Nakrani]

Describe the bug
_n() function mocker always returns the first string (singular) regardless number passed in the argument list.

The reason for the behaviour is mocker here function-mocks.php#L159 uses predefined_return_function_helper that always first item from the arguments array.

To Reproduce
Below is the code that produces the error.

public function test_check_n_output_wp_mock() {
	$output = check_n_output_wp_mock();
	$this->assertEquals( 'People', $output );
}

It returns Person instead of People

code being tested:

function check_n_output_wp_mock() {
	return _n( 'Person', 'People', 3 );
}

Expected behaviour

_n() Mocker should the singular or plural form based on the supplied number.