public function testCallStatic()
 {
     $factory = m::mock('Omnipay\\Common\\GatewayFactory');
     $factory->shouldReceive('testMethod')->with('some-argument')->once()->andReturn('some-result');
     Omnipay::setFactory($factory);
     $result = Omnipay::testMethod('some-argument');
     $this->assertSame('some-result', $result);
 }