<phpunit>
  <testsuites>
    <testsuite name="Unit test">
      <directory>tests</directory>
    </testsuite>
  </testsuites>
  <filter>
  <whitelist processUncoveredFilesFromWhitelist="true">
    <directory>.</directory>
    </whitelist>
  </filter>
  <logging>
    <log type="coverage-clover" target="clover.xml"/>
  </logging>
</phpunit>

<phpunit>
  <testsuites>
    <testsuite name="Unit test">
      <directory>tests</directory>
    </testsuite>
  </testsuites>
  <filter>
    <whitelist processUncoveredFilesFromWhitelist="true">
      <directory>.</directory>
      <exclude>
        <directory>tests</directory>
      </exclude>
    </whitelist>
  </filter>
  <logging>
    <log type="coverage-clover" target="clover.xml"/>
  </logging>
</phpunit>

Exclude white listing the tests directory.
Exclude white listing the tests directory.