TEST(RegexMatchExpression, MatchesElementSymbolType) {
    BSONObj match = BSONObjBuilder().appendSymbol("x", "yz").obj();
    BSONObj notMatch = BSONObjBuilder().appendSymbol("x", "gg").obj();
    RegexMatchExpression regex("", "yz", "");
    ASSERT(regex.matchesSingleElement(match.firstElement()));
    ASSERT(!regex.matchesSingleElement(notMatch.firstElement()));
}
TEST(RegexMatchExpression, MatchesElementSymbolType) {
    BSONObj match = BSONObjBuilder().appendSymbol("x", "yz").obj();
    BSONObj notMatch = BSONObjBuilder().appendSymbol("x", "gg").obj();
    RegexMatchExpression regex("", "yz", "");
    ASSERT(regex.matchesSingleElement(match.firstElement()));
    ASSERT(!regex.matchesSingleElement(notMatch.firstElement()));
}