code: private void loadImplementationsInDirectory(final Test test, final String parent, final File location) {
          final File[] files = location.listFiles();
          if (files == null) {
              return;
          }
  
          StringBuilder builder;
          for (final File file : files) {
              builder = new StringBuilder();
              builder.append(parent).append('/').append(file.getName());
              final String packageOrClass = parent == null ? file.getName() : builder.toString();
  
              if (file.isDirectory()) {
                  loadImplementationsInDirectory(test, packageOrClass, file);
              } else if (isTestApplicable(test, file.getName())) {
                  addIfMatching(test, packageOrClass);
              }
          }
      }
docs: Finds matches in a physical directory on a filesystem. Examines all files within a directory - if the File object
  is not a directory, and ends with <i>.class</i> the file is loaded and tested to see if it is acceptable
  according to the Test. Operates recursively to find classes within a folder structure matching the package
  structure.
  
  @param test
  a Test used to filter the classes that are discovered
  @param parent
  the package name up to this directory in the package hierarchy. E.g. if /classes is in the classpath and
  we wish to examine files in /classes/org/apache then the values of <i>parent</i> would be
  <i>org/apache</i>
  @param location
  a File object representing a directory