private static String extractMockitoExceptionMessage(MockitoException ex) {
    Throwable exToUse = ex;
    if (ex.getCause() instanceof InstantiationException) {
      exToUse = ex.getCause();
    }
    return exToUse.getMessage().trim();
  }
Resolves the inline mock maker of Mockito, via different ways, depending on the Mockito version.

@return The inline mock maker of Mockito
spock-core/src/main/java/org/spockframework/mock/runtime/mockito/MockitoMockMakerImpl.java