Catching PHP errors with simpleTest

I needed to write a test that should fail if the method I was testing triggered a PHP E_NOTICE error (namely, an "undefined index" kind of error).

SimpleTest provides both expectError() and expectException() methods. I have only been able to make the former work with manually triggered errors (using trigger_error()), and the latter only catchs Exceptions.

After hours of googling, and reading SimpleTest source code, I finally managed to come up with a solution.

Redefining the error handler

It still amaze me how awfuly complicated it is to do such a simple thing. Anyway, the key is to redefine the error handler function so you can shortcircuit both PHP and SimpleTest on the way they managed errors.

Doing so you can detect when the code you test produce an error. Based on the $errno and $errstr supplied, you can even filter to exactly the error you're looking for.

Unfortunatly, you'll be blocked inside your newly defined error_handler function. It means you won't have access to the test, so won't be able to call $this->pass() nor $this->fail(), because $this does not reference anything.

Throw me out of here

The only trick I've found to get out of this function and back in the scope of your test is to throw an Exception. Namely, an ErrorException.

Doing so we can rewrote our test to put the part that is triggering the error inside a try/ catchstatement and manually pass or fail the test.

Don't you forget something ?

One very important thing not to forget here is to restore the error_handler to its original value once you won't need it. If you don't, you will surely broke all your subsequent tests because SimpleTest use its own error_handler too.

We have to restore it in two places, both when the code triggered and error / throw an exception and when it don't.

Cut the speech, show me the code

Okay, here's the code. Don't forget to adapt the condition in the error_handler to match your error.

function testGotUndefinedIndex() {
    // Overriding the error handler
    function errorHandlerCatchUndefinedIndex($errno, $errstr, $errfile, $errline ) {
        // We are only interested in one kind of error
        if ($errstr=='Undefined index: bar') {
            //We throw an exception that will be catched in the test
            throw new ErrorException($errstr, 0, $errno, $errfile, $errline);
        return false;

    try {
        // triggering the error
        $foo = array();
        echo $foo['bar'];
    } catch (ErrorException $e) {
        // Very important : restoring the previous error handler
        // Manually asserting that the test fails

    // Very important : restoring the previous error handler
    // Manually asserting that the test succeed

Tags : #errors #unit-testing #simpletest #e-notice

Want to add something ? Feel free to get in touch on Twitter : @pixelastic