[WIP] Fix unit tests

Running the `bin/pre-commit` hook which ends in:

```bash
phpunit --filter WordPress "$phpcs_root/tests/AllTests.php"
```

Or navigating to the PHPCS install directory and running `phpunit` from there, both result in the following:

```
$ phpunit --filter WordPress tests/AllTests.php

PHPUnit 4.0.7 by Sebastian Bergmann.

The Xdebug extension is not loaded. No code coverage will be generated.



Time: 128 ms, Memory: 22.00Mb

No tests executed!
```

It seems that PHP_CodeSniffer is not looking for standards installed in other locations when running the unit tests, so the `--filter WordPress` is resulting in nothing matching. We may need to open an issue/PR on PHP_CodeSniffer itself, but I wanted to see if we could fix it internally first.

Any ideas?