Call protected/private static method of a class. Used usually in Unit Test.

MethodInvoker.php

<?php
trait MethodInvoker {
    /**
     * Call protected/private static method of a class.
     *
     * @param string $class - class name that we will run method on
     * @param string $methodName - method name to call
     * @param array  $parameter - parameter to pass into method
     *
     * @return mixed - original method's return
     */
    public static function invokeStaticMethod($class, $methodName)
    {
        $reflectionClass = new ReflectionClass($class);
        $method = $reflectionClass->getMethod($methodName);
        $method->setAccessible(true);

        // get all the parameters after $methodName
        $parameters = array_slice(func_get_args(), 2);

        return $method->invokeArgs(null, $parameters);
    }
}

Example:

class OpenSearch_AppTest extends PHPUnit_Framework_TestCase {
    use MethodInvoker;

    public function testGetIndexConfigs() {
        $expected = [];
        $actual = $this->invokeStaticMethod('OpenSearch_App', 'getIndexConfigs', $searchFields);

        $this->assertEquals($expected, $actual);
    }
}