diff --git a/test/string/utf/utf.cmake b/test/string/utf/utf.cmake
index 7b5512a..26c2b41 100644
--- a/test/string/utf/utf.cmake
+++ b/test/string/utf/utf.cmake
@@ -1,8 +1,10 @@
 # See the end of this file for copyright and license terms.
 
 target_sources(neo_test PRIVATE
+    string/utf/utf8_check.cpp
     string/utf/utf8_chrsize.cpp
     string/utf/utf8_from_nchr.cpp
+    string/utf/utf8_strlen.cpp
     string/utf/utf8_to_nchr.cpp
 )
 
diff --git a/test/string/utf/utf8_check.cpp b/test/string/utf/utf8_check.cpp
new file mode 100644
index 0000000..8d6c110
--- /dev/null
+++ b/test/string/utf/utf8_check.cpp
@@ -0,0 +1,124 @@
+/** See the end of this file for copyright and license terms. */
+
+#include <catch2/catch.hpp>
+#include <errno.h>
+
+#include <neo.h>
+#include <neo/utf.h>
+
+TEST_CASE( "utf8_check: ASCII string", "[string/utf.c]" )
+{
+	error err;
+	utf8_check("i'm gay,,,", &err);
+
+	REQUIRE( errnum(&err) == 0 );
+	REQUIRE( errmsg(&err) == nil );
+}
+
+TEST_CASE( "utf8_check: String with 2-byte UTF-8 sequence", "[string/utf.c]" )
+{
+	error err;
+	/* U+03B1 Greek Smol Letter Alpha */
+	utf8_check("i'm g\xce\xb1y,,,", &err);
+
+	REQUIRE( errnum(&err) == 0 );
+	REQUIRE( errmsg(&err) == nil );
+}
+
+TEST_CASE( "utf8_check: String with 3-byte UTF-8 sequence", "[string/utf.c]" )
+{
+	error err;
+	/* U+3042 Hiragana Letter A */
+	utf8_check("i'm g\xe3\x81\x82y,,,", &err);
+
+	REQUIRE( errnum(&err) == 0 );
+	REQUIRE( errmsg(&err) == nil );
+}
+
+TEST_CASE( "utf8_check: String with 4-byte UTF-8 sequence", "[string/utf.c]" )
+{
+	error err;
+	/* U+1F97A The Bottom Emoji(TM) */
+	utf8_check("i'm gay\xf0\x9f\xa5\xba,,,", &err);
+
+	REQUIRE( errnum(&err) == 0 );
+	REQUIRE( errmsg(&err) == nil );
+}
+
+TEST_CASE( "utf8_check: Error on malformed sequence start", "[string/utf.c]" )
+{
+	error err;
+	utf8_check("\xff", &err);
+
+	string *expected = nstr("Illegal UTF-8 sequence start byte: 0xff", nil);
+	string *actual = errmsg(&err);
+
+	REQUIRE( errnum(&err) == EINVAL );
+	REQUIRE( nstreq(expected, actual, nil) );
+	errput(&err);
+}
+
+TEST_CASE( "utf8_check: Error on wrong second byte", "[string/utf.c]" )
+{
+	error err;
+	utf8_check("\xce\xff", &err);
+
+	string *expected = nstr("Byte 2 in UTF-8 sequence invalid: 0xff", nil);
+	string *actual = errmsg(&err);
+
+	REQUIRE( errnum(&err) == EINVAL );
+	REQUIRE( nstreq(expected, actual, nil) );
+	errput(&err);
+}
+
+TEST_CASE( "utf8_check: Error on wrong third byte", "[string/utf.c]" )
+{
+	error err;
+	utf8_check("\xe3\x81\xff", &err);
+
+	string *expected = nstr("Byte 3 in UTF-8 sequence invalid: 0xff", nil);
+	string *actual = errmsg(&err);
+
+	REQUIRE( errnum(&err) == EINVAL );
+	REQUIRE( nstreq(expected, actual, nil) );
+	errput(&err);
+}
+
+TEST_CASE( "utf8_check: Error on wrong fourth byte", "[string/utf.c]" )
+{
+	error err;
+	utf8_check("\xf0\x9f\xa5\xff", &err);
+
+	string *expected = nstr("Byte 4 in UTF-8 sequence invalid: 0xff", nil);
+	string *actual = errmsg(&err);
+
+	REQUIRE( errnum(&err) == EINVAL );
+	REQUIRE( nstreq(expected, actual, nil) );
+	errput(&err);
+}
+
+TEST_CASE( "utf8_check: Error on non canonical encoding", "[string/utf.c]" )
+{
+	error err;
+	utf8_check("\xf0\x80\x80\xa0", &err);
+
+	string *expected = nstr("Non canonical UTF-8 encoding: 1 byte character stored in 4 bytes", nil);
+	string *actual = errmsg(&err);
+
+	REQUIRE( errnum(&err) == EINVAL );
+	REQUIRE( nstreq(expected, actual, nil) );
+	errput(&err);
+}
+
+/*
+ * This file is part of libneo.
+ * Copyright (c) 2021 Fefie <owo@fef.moe>.
+ *
+ * libneo is non-violent software: you may only use, redistribute,
+ * and/or modify it under the terms of the CNPLv6+ as found in
+ * the LICENSE file in the source code root directory or at
+ * <https://git.pixie.town/thufie/CNPL>.
+ *
+ * libneo comes with ABSOLUTELY NO WARRANTY, to the extent
+ * permitted by applicable law.  See the CNPLv6+ for details.
+ */
diff --git a/test/string/utf/utf8_strlen.cpp b/test/string/utf/utf8_strlen.cpp
new file mode 100644
index 0000000..488c7f2
--- /dev/null
+++ b/test/string/utf/utf8_strlen.cpp
@@ -0,0 +1,41 @@
+/** See the end of this file for copyright and license terms. */
+
+#include <catch2/catch.hpp>
+#include <errno.h>
+
+#include <neo.h>
+#include <neo/utf.h>
+
+TEST_CASE( "utf8_strlen: ASCII string", "[string/utf.c]" )
+{
+	usize len = utf8_strlen("i'm gay,,,");
+
+	REQUIRE( len == 10 );
+}
+
+TEST_CASE( "utf8_strlen: UTF-8 string", "[string/utf.c]" )
+{
+	usize len = utf8_strlen("i'm gay\xf0\x9f\xa5\xba,,,");
+
+	REQUIRE( len == 11 );
+}
+
+TEST_CASE( "utf8_strlen: Empty string", "[string/utf.c]" )
+{
+	usize len = utf8_strlen("");
+
+	REQUIRE( len == 0 );
+}
+
+/*
+ * This file is part of libneo.
+ * Copyright (c) 2021 Fefie <owo@fef.moe>.
+ *
+ * libneo is non-violent software: you may only use, redistribute,
+ * and/or modify it under the terms of the CNPLv6+ as found in
+ * the LICENSE file in the source code root directory or at
+ * <https://git.pixie.town/thufie/CNPL>.
+ *
+ * libneo comes with ABSOLUTELY NO WARRANTY, to the extent
+ * permitted by applicable law.  See the CNPLv6+ for details.
+ */