public function testRegisterErrorHandler()
{
$writer = new MockWriter();
$this->logger->addWriter($writer);
$this->assertTrue(Logger::registerErrorHandler($this->logger));
// check for single error handler instance
$this->assertFalse(Logger::registerErrorHandler($this->logger));
// generate a warning
echo $test;
Logger::unregisterErrorHandler();
$this->assertEquals($writer->events[0]['message'], 'Undefined variable: test');
}