### Question:
LearningRule implements Serializable { public synchronized void removeListener(LearningEventListener listener) { if (listener == null) throw new IllegalArgumentException("listener is null!"); listeners.remove(listener); } LearningRule(); void setTrainingSet(DataSet trainingSet); DataSet getTrainingSet(); NeuralNetwork getNeuralNetwork(); void setNeuralNetwork(NeuralNetwork neuralNetwork); synchronized void stopLearning(); synchronized boolean isStopped(); synchronized void addListener(LearningEventListener listener); synchronized void removeListener(LearningEventListener listener); abstract void learn(DataSet trainingSet);  }### Answer:
@Test(expected = IllegalArgumentException.class) public void testRemoveListenerThrowExceptionIfListerNull() { testableLearningRule.removeListener(null); }