TestSuite testerSuite =
          makeSuiteForTesterClass((Class<? extends AbstractTester<?>>) testerClass);
      if (testerSuite.countTestCases() > 0) {
        suite.addTest(testerSuite);
      }
    }
    return suite;
  }

  /** Throw {@link IllegalStateException} if {@link #createTestSuite()} can't be called yet. */