def confusion_stats(set_true, set_test):
    """
    Count the true positives, false positives and false
    negatives in a test set with respect to a "true" set. 
    True negatives are not counted.
    """
    true_pos = len(set_true.intersection(set_test))
    false_pos = len(set_test.difference(set_true))
    false_neg = len(set_true.difference(set_test))
    
    return true_pos, false_pos, false_neg