If you use Maven with the surefire-test plugin, its default filter setting for searching test classes is to skip inner classes:

<excludes>
   <exclude>**/*$*</exclude>
</excludes>

In case when you have inner classes defined in your JUnit TestCases and you have configured a Surefire plugin to run your inner classes as well, you might get an error like this:

 -------------------------------------------------------------------------------
 Test set: TestUtils$__CLR2_6_34a4agh7gevmc
 -------------------------------------------------------------------------------
 Tests run: 2, Failures: 0, Errors: 2, Skipped: 0, Time elapsed: 0.094 sec <<< FAILURE!
 initializationError(TestUtils$__CLR2_6_34a4agh7gevmc) Time elapsed: 0.016 sec <<< ERROR!
 java.lang.Exception: Test class should have exactly one public constructor
 at org.junit.runners.BlockJUnit4ClassRunner.validateOnlyOneConstructor(BlockJUnit4ClassRunner.java:143)

This is because Clover generates inner class for each class (test or application code). In order to fix a problem, you have to change your pom.xml and filter out from your test scope any inner classes beginning with __CLR.

For example:

<build>
  <plugins>
    <plugin>
      <groupId>org.apache.maven.plugins</groupId>
      <artifactId>maven-surefire-plugin</artifactId>
      <properties>
        <excludes>
          <exclude>**/*$__CLR*</exclude>
        </excludes>
      </properties>
    </plugin>
  </plugins>
</build>