utf8len
ssize_t utf8len(struct tree *, const char *);
KUNIT_EXPECT_EQ(test, utf8len(um, UTF8_NFDI, nfdi_test_data[i].str), nlen);
KUNIT_EXPECT_EQ(test, utf8len(um, UTF8_NFDICF, nfdicf_test_data[i].str),