xUnit does not read the following output with nested <testsuite>-tags from PHPUnit:

<testsuites>
<testsuite name="src/webroot/trackstar/protected/tests/unit" tests="1" assertions="2" failures="0" errors="0" time="0.032417">
<testsuite name="DbTest" file="src/protected/tests/unit/DbTest.php" tests="1" assertions="2" failures="0" errors="0" time="0.032417">
<testcase name="testConnection" class="DbTest" file="src/protected/tests/unit/DbTest.php" line="4" assertions="2" time="0.032417"/>
</testsuite>
</testsuite>
</testsuites>

The version without nested tags works:

<testsuites>
<testsuite name="DbTest" file="src/protected/tests/unit/DbTest.php" tests="1" assertions="2" failures="0" errors="0" time="0.032417">
<testcase name="testConnection" class="DbTest" file="src/protected/tests/unit/DbTest.php" line="4" assertions="2" time="0.032417"/>
</testsuite>
</testsuites>

I think it would be nice, if xUnit supports nested <testsuite>-tags. The workaround with a xlst is somehow cumbersome.