Additional unit test classes in a single test class are never tested

Noticed whilst writing some additional tests for backup/util/dbops/tests/dbops_test.php

There are two classes in dbops_test.php, each with valid test cases.
Running vendor/bin/phpunit in a variety of ways only tests the first class, and not subsequent classes.

Specify by file:

vendor/bin/phpunit backup/util/dbops/tests/dbops_test.php

Edit phpunit.xml and remove all testsuites. Add the following instead:

    <testsuites>

        <testsuite name="core_backup">

          <directory suffix="_test.php">backup/util/dbops</directory>

        </testsuite>

    </testsuites>

Now run:

vendor/bin/phpunit --testsuite core_backup

Or even:

vendor/bin/phpunit

You'll notice that each of these only runs a single test, with 19 assertions. None of the tests in the second class are tested at all.

This also happens for lib/tests/pagelib_test.php. I suspect that there are other places where multiple tests exist in the same file, but I've not tested.