### Question:
Layer implements Iterable<Neuron>, Serializable { public int indexOf(Neuron neuron) { return neurons.indexOf(neuron); } Layer();  Layer(int neuronsCount);  Layer(int neuronsCount, NeuronProperties neuronProperties); final void setParentNetwork(NeuralNetwork parent); final NeuralNetwork getParentNetwork(); final List<Neuron> getNeurons(); final void addNeuron(Neuron neuron); final void addNeuron(int index, Neuron neuron); final void setNeuron(int index, Neuron neuron); final void removeNeuron(Neuron neuron); final void removeNeuronAt(int index); final void removeAllNeurons(); Neuron getNeuronAt(int index); int indexOf(Neuron neuron); int getNeuronsCount(); void calculate(); void reset(); void initializeWeights(double value); String getLabel(); void setLabel(String label); boolean isEmpty(); @Override Iterator<Neuron> iterator();  }### Answer:
@Test public void testIndexOf() { assertEquals(instance.indexOf(testneuron1), 0); assertEquals(instance.indexOf(testneuron2), 1); }