@Test
  public void returnsConnectionBetweenTwoLayers() {
    Set<Layer> layers = new HashSet<Layer>();
    Layer topLayer = new Layer();
    Layer middleLayer = new Layer();

    Connections firstConnection = new FullyConnected(topLayer, middleLayer, 0, 0);

    topLayer.addConnection(firstConnection);

    layers.add(topLayer);
    layers.add(middleLayer);
    network.setLayers(layers);

    assertEquals(firstConnection, network.getConnection(topLayer, middleLayer));
    assertEquals(firstConnection, network.getConnection(middleLayer, topLayer));
  }
  @Test
  public void returnsNullWhenThereIsntAConnectingLayer() {
    Set<Layer> layers = new HashSet<Layer>();
    Layer topLayer = new Layer();
    Layer middleLayer = new Layer();
    Layer bottomLayer = new Layer();

    Connections firstConnection = new FullyConnected(topLayer, middleLayer, 0, 0);

    topLayer.addConnection(firstConnection);

    layers.add(topLayer);
    layers.add(middleLayer);
    network.setLayers(layers);

    assertNull(network.getConnection(topLayer, bottomLayer));
    assertNull(network.getConnection(bottomLayer, topLayer));
  }