PHP Unit Tests: Is it possible to test for a Fatal Error?

No. Fatal error stops the execution of the script.

And it's not really necessary to test a singleton in that way. If you insist on checking if constructor is private, you can use ReflectionClass:getConstructor()

public function testCannotInstantiateExternally(){    $reflection = new \ReflectionClass('\My\Namespace\MyClassName');    $constructor = $reflection->getConstructor();    $this->assertFalse($constructor->isPublic());}

Another thing to consider is that Singleton classes/objects are an obstacle in TTD since they're difficult to mock.

Here's a complete code snippet of Mchl's answer so people don't have to go through the docs...

public function testCannotInstantiateExternally(){    $reflection = new \ReflectionClass('\My\Namespace\MyClassName');    $constructor = $reflection->getConstructor();    $this->assertFalse($constructor->isPublic());}

You can use a concept like PHPUnit's process-isolation.

This means the test code will be executed in a sub process of php. This example shows how this could work.

<?php// get the test code as string$testcode = '<?php new '; // will cause a syntax error// put it in a temporary file$testfile = tmpfile();file_put_contents($testfile, $testcode);exec("php $tempfile", $output, $return_value);// now you can process the scripts return value and output// in case of an syntax error the return value is 255switch($return_value) {    case 0 :        echo 'PASSED';        break;    default :        echo 'FAILED ' . $output;}// clean upunlink($testfile);