### Question:
Layer implements Iterable<Neuron>, Serializable { public final void setNeuron(int index, Neuron neuron) { Objects.requireNonNull(neuron, "Neuron can't be null!"); neurons.set(index, neuron); neuron.setParentLayer(this); if (parentNetwork != null) parentNetwork.fireNetworkEvent(new NeuralNetworkEvent(neuron, NeuralNetworkEvent.Type.NEURON_ADDED)); } 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 testSetNeuron() { instance.setNeuron(1, testneuron3); List<Neuron> lst = instance.getNeurons(); assertEquals(testneuron3, lst.get(1)); }