def METHOD_NAME(self):
    """Test that the tree contains only Node subclasses."""
    def inspect(node):
        """Inspect node children."""
        for child in node.children:
            self.assertTrue(isinstance(child, Node))
            inspect(child)
    # Test the canonical example file.
    qasm = Qasm(self.qasm_file_path)
    res = qasm.parse()
    inspect(res)
    # Test a file containing if instructions.
    qasm_if = Qasm(self.qasm_file_path_if)
    res_if = qasm_if.parse()
    inspect(res_if)