boolean isMapped(String userId) {
        return idToDirectoryNameMap.containsKey(getIdStrategy().keyFor(userId));
    }
@Test
    public void testDuplicatedUserId() throws IOException {
        UserIdMapper mapper = createUserIdMapper(IdStrategy.CASE_INSENSITIVE);
        assertThat(mapper.isMapped("user2"), is(true));
        assertThat(mapper.isMapped("user1"), is(true));
    }