fix test utils

[ZZZank]

• Utils#assertException(int, Class, String, String) was doing nothing, because it has no method body:

    public static <T extends Exception> void assertException(
            final int languageVersion,
            final Class<T> expectedThrowable,
            final String expectedMessage,
            String js) {}

• There's also a new helper function Utils#lines(String[]) to make writing multi-line scripts easier. Utils.lines("line1", "line2", "line3") equals to "line1\n" + "line2\n" + "line3"

[gbrail]

This seems helpful and fine to me. Any thoughts from others? Otherwise I'll merge it soon.

[rbri]

+1

[gbrail]

Thanks for doing this!