PHPUnit working in IDE, but server says class not found

I ran into the same problem and if you are not too familiar with the inner workings of both PHPUnit and Composer this can indeed seem perplexing.

PHPunit does not use use the Composer autoloader to find any of your test classes. It just scans any directory you give it and operates on one file at a time.

Hence it does not know about any other class than the one in the file it is currently operating on. That is where the bootstrap file comes into play.

If you want to use the Composer Autoloader to load other test classes, you need to tell it where it can find these test classes (and, optionally, in which namespace).

There are two ways to do this:

1. Add an autoload-dev section to your composer.json or
2. Add the test directory to the Composer Autoloader

Use autoload-dev

The autoload-dev sections allows you to define autoload rules for development purposes.

Quoting directly from the manual:

Classes needed to run the test suite should not be included in the main autoload rules to avoid polluting the autoloader in production and when other people use your package as a dependency.

Therefore, it is a good idea to rely on a dedicated path for your unit tests and to add it within the autoload-dev section.

Example:

{
    "autoload": {
        "psr-4": { "MyLibrary\": "src/" }
    },
    "autoload-dev": {
        "psr-4": { "MyLibrary\Tests\": "tests/" }
    }
}

Add to the Composer Autoloader

An alternative would be to get the Composer Autoloader and add your testing namespace (if you have any) and the directory where your tests live. How to do this, as described in the manual (at the bottom of the autoloading section in "Basic Usage") is :

$loader = require('/path/to/vendor/autoload.php');
$loader->add('Test\', __DIR__ . '/Tests');

If your tests use namespaces that mirror the test directory and you still run into trouble, you can try omitting the prefix by replacing the first parameter ('Test\') with ''.

If you want further insight into how all of this works you should take a look at the Composer ClassLoader class, especially the add() and findFile() methods.

On Mac OS X environment variables available in Terminal and for the normal applications can be different, check the related question for the solution how to make them similar.

Note that this solution will not work on Mountain Lion (10.8).