phpunit processes only a single file instead of multiple

My tests folder looks like this:

- Tests
- folder
-- classTest.php
- anotherClassTest.php

Before I'd created folder/classTest.php, PHPUnit tested to anotherClassTest.php perfectly but since I've added folder/classTest.php it only tests that one and does no longer test anotherClassTest.php.

My config looks like this:

<?xml version="1.0" encoding="UTF-8"?>
<phpunit
        strict="true"
        bootstrap="./Tests/Bootstrap.php"
>
    <testsuites>
        <testsuite name="unit">
            <directory>Tests/*</directory>
        </testsuite>
    </testsuites>
    <logging>
        <log type="testdox-html" target="Tests/results.html"/>
    </logging>
    <filter>
        <blacklist>
            <directory suffix=".php">vendor</directory>
        </blacklist>
        <whitelist processUncoveredFilesFromWhitelist="true">
            <directory suffix=".php">Tests/</directory>
        </whitelist>
    </filter>
</phpunit>

What is going wrong here?