Index: uspace/lib/c/test/main.c
===================================================================
--- uspace/lib/c/test/main.c	(revision 2ef2a0d9847a69ef400b4e5171b00b11e38ae2db)
+++ uspace/lib/c/test/main.c	(revision f167c851099aef2600cce71c5e10cc3f3dc8ee11)
@@ -57,4 +57,5 @@
 PCUT_IMPORT(strtol);
 PCUT_IMPORT(table);
+PCUT_IMPORT(uchar);
 PCUT_IMPORT(uuid);
 
Index: uspace/lib/c/test/uchar.c
===================================================================
--- uspace/lib/c/test/uchar.c	(revision f167c851099aef2600cce71c5e10cc3f3dc8ee11)
+++ uspace/lib/c/test/uchar.c	(revision f167c851099aef2600cce71c5e10cc3f3dc8ee11)
@@ -0,0 +1,167 @@
+/*
+ * Copyright (c) 2025 Jiří Zárevúcky
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ * - Redistributions in binary form must reproduce the above copyright
+ *   notice, this list of conditions and the following disclaimer in the
+ *   documentation and/or other materials provided with the distribution.
+ * - The name of the author may not be used to endorse or promote products
+ *   derived from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+ * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+ * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <mem.h>
+#include <pcut/pcut.h>
+#include <stdio.h>
+#include <uchar.h>
+
+PCUT_INIT;
+
+PCUT_TEST_SUITE(uchar);
+
+PCUT_TEST(mbrtoc16)
+{
+	mbstate_t mbstate;
+	memset(&mbstate, 0, sizeof(mbstate));
+
+	size_t ret;
+	const char *s = u8"a𐎣";
+	char16_t out[] = u"AAAAA";
+	const char16_t expected[] = u"a𐎣";
+
+	ret = mbrtoc16(&out[0], s, MB_CUR_MAX, &mbstate);
+	PCUT_ASSERT_INT_EQUALS(1, ret);
+	PCUT_ASSERT_INT_EQUALS(expected[0], out[0]);
+
+	s += ret;
+
+	ret = mbrtoc16(&out[1], s, MB_CUR_MAX, &mbstate);
+	PCUT_ASSERT_INT_EQUALS(4, ret);
+	PCUT_ASSERT_INT_EQUALS(expected[1], out[1]);
+
+	s += ret;
+
+	ret = mbrtoc16(&out[2], s, MB_CUR_MAX, &mbstate);
+	PCUT_ASSERT_INT_EQUALS(-3, ret);
+	PCUT_ASSERT_INT_EQUALS(expected[2], out[2]);
+
+	ret = mbrtoc16(&out[3], s, MB_CUR_MAX, &mbstate);
+	PCUT_ASSERT_INT_EQUALS(0, ret);
+	PCUT_ASSERT_INT_EQUALS(expected[3], out[3]);
+}
+
+PCUT_TEST(c16rtomb)
+{
+	mbstate_t mbstate;
+	memset(&mbstate, 0, sizeof(mbstate));
+
+	const char16_t in[] = u"aβℷ𐎣";
+	char out[] = "AAAAAAAAAAAAAAAAA";
+
+	char *s = out;
+
+	for (size_t i = 0; i < sizeof(in) / sizeof(char16_t); i++) {
+		s += c16rtomb(s, in[i], &mbstate);
+	}
+
+	const char expected[] = u8"aβℷ𐎣";
+	PCUT_ASSERT_STR_EQUALS(expected, out);
+	PCUT_ASSERT_INT_EQUALS(s - out, sizeof(expected));
+}
+
+PCUT_TEST(mbrtoc32)
+{
+	mbstate_t mbstate;
+	memset(&mbstate, 0, sizeof(mbstate));
+
+	size_t ret;
+	char32_t c = 0;
+	const char *s = u8"aβℷ𐎣";
+
+	ret = mbrtoc32(&c, s, MB_CUR_MAX, &mbstate);
+	PCUT_ASSERT_INT_EQUALS(ret, 1);
+	PCUT_ASSERT_INT_EQUALS(c, U'a');
+
+	s += ret;
+
+	ret = mbrtoc32(&c, s, 1, &mbstate);
+	PCUT_ASSERT_INT_EQUALS(ret, -2);
+	PCUT_ASSERT_INT_EQUALS(c, U'a');
+
+	s += 1;
+
+	ret = mbrtoc32(&c, s, MB_CUR_MAX, &mbstate);
+	PCUT_ASSERT_INT_EQUALS(ret, 1);
+	PCUT_ASSERT_INT_EQUALS(c, U'β');
+
+	s += ret;
+
+	ret = mbrtoc32(&c, s, MB_CUR_MAX, &mbstate);
+	PCUT_ASSERT_INT_EQUALS(ret, 3);
+	PCUT_ASSERT_INT_EQUALS(c, U'ℷ');
+
+	s += ret;
+
+	ret = mbrtoc32(&c, s, 3, &mbstate);
+	PCUT_ASSERT_INT_EQUALS(ret, -2);
+	PCUT_ASSERT_INT_EQUALS(c, U'ℷ');
+
+	s += 3;
+
+	ret = mbrtoc32(&c, s, MB_CUR_MAX, &mbstate);
+	PCUT_ASSERT_INT_EQUALS(ret, 1);
+	PCUT_ASSERT_INT_EQUALS(c, U'𐎣');
+
+	s += ret;
+
+	ret = mbrtoc32(&c, s, MB_CUR_MAX, &mbstate);
+	PCUT_ASSERT_INT_EQUALS(ret, 0);
+	PCUT_ASSERT_INT_EQUALS(c, 0);
+}
+
+PCUT_TEST(c32rtomb)
+{
+	mbstate_t mbstate;
+	memset(&mbstate, 0, sizeof(mbstate));
+
+	char out[] = "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA";
+	char *s = out;
+
+	_Static_assert(sizeof(out) > 5 * MB_CUR_MAX);
+
+	s += c32rtomb(s, U'a', &mbstate);
+	PCUT_ASSERT_INT_EQUALS(s - out, 1);
+
+	s += c32rtomb(s, U'β', &mbstate);
+	PCUT_ASSERT_INT_EQUALS(s - out, 3);
+
+	s += c32rtomb(s, U'ℷ', &mbstate);
+	PCUT_ASSERT_INT_EQUALS(s - out, 6);
+
+	s += c32rtomb(s, U'𐎣', &mbstate);
+	PCUT_ASSERT_INT_EQUALS(s - out, 10);
+
+	s += c32rtomb(s, 0, &mbstate);
+	PCUT_ASSERT_INT_EQUALS(s - out, 11);
+
+	const char expected[] = u8"aβℷ𐎣";
+	PCUT_ASSERT_INT_EQUALS(memcmp(out, expected, sizeof(expected)), 0);
+}
+
+PCUT_EXPORT(uchar);