def WebIDLTest(parser, harness):
    threw = False
    try:
        parser.parse(
            """
            interface OptionalConstraints1 {
              undefined foo(optional byte arg1, byte arg2);
            };
        """
        )

        parser.finish()
    except Exception:
        threw = True

    harness.ok(
        not threw,
        "Should not have thrown on non-optional argument following "
        "optional argument.",
    )

    parser = parser.reset()
    parser.parse(
        """
        interface OptionalConstraints2 {
          undefined foo(optional byte arg1 = 1, optional byte arg2 = 2,
                        optional byte arg3, optional byte arg4 = 4,
                        optional byte arg5, optional byte arg6 = 9);
        };
    """
    )
    results = parser.finish()
    args = results[0].members[0].signatures()[0][1]
    harness.check(len(args), 6, "Should have 6 arguments")
    harness.check(args[5].defaultValue.value, 9, "Should have correct default value")
