### Question:
PairNode extends Node { public Node getKey() { return key; } PairNode(Node key, Node value);  PairNode(GyroParser.PairContext context); Node getKey(); Node getValue(); @Override R accept(NodeVisitor<C, R, X> visitor, C context);  }### Answer:
@Test void getKey() { Node keyNode = mock(Node.class); PairNode node = new PairNode(keyNode, mock(Node.class)); assertThat(node.getKey()).isEqualTo(keyNode); }