Index: uspace/lib/c/test/main.c
===================================================================
--- uspace/lib/c/test/main.c	(revision ea4910bfed05043e6107a7bf8389ce3e6adfcf37)
+++ uspace/lib/c/test/main.c	(revision 7e85d2be0102c8f5b4a85409e870435ac1c03f11)
@@ -37,4 +37,5 @@
 PCUT_IMPORT(mem);
 PCUT_IMPORT(odict);
+PCUT_IMPORT(perf);
 PCUT_IMPORT(perm);
 PCUT_IMPORT(qsort);
Index: uspace/lib/c/test/perf.c
===================================================================
--- uspace/lib/c/test/perf.c	(revision 7e85d2be0102c8f5b4a85409e870435ac1c03f11)
+++ uspace/lib/c/test/perf.c	(revision 7e85d2be0102c8f5b4a85409e870435ac1c03f11)
@@ -0,0 +1,80 @@
+/*
+ * Copyright (c) 2018 Vojtech Horky
+ * 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 <pcut/pcut.h>
+#include <fibril.h>
+#include <perf.h>
+
+PCUT_INIT;
+
+PCUT_TEST_SUITE(perf);
+
+/* Checks that initialization zeroes out all entries. */
+PCUT_TEST(zero_diff)
+{
+	stopwatch_t sw;
+	stopwatch_init(&sw);
+	PCUT_ASSERT_INT_EQUALS(0, (int) stopwatch_get_nanos(&sw));
+}
+
+/* Checks that initialization zeroes out all entries. */
+PCUT_TEST(zero_diff_static)
+{
+	stopwatch_t sw = STOPWATCH_INITIALIZE_STATIC;
+	PCUT_ASSERT_INT_EQUALS(0, (int) stopwatch_get_nanos(&sw));
+}
+
+/* Checks that measuring 1s sleep does not give completely invalid results. */
+PCUT_TEST(stopwatch_smokes)
+{
+	stopwatch_t sw = STOPWATCH_INITIALIZE_STATIC;
+	stopwatch_start(&sw);
+	fibril_sleep(1);
+	stopwatch_stop(&sw);
+	nsec_t diff_nanos = stopwatch_get_nanos(&sw);
+	PCUT_ASSERT_TRUE(diff_nanos > MSEC2NSEC(500));
+	PCUT_ASSERT_TRUE(diff_nanos < SEC2NSEC(5));
+}
+
+/* Checks that setting time works for small values. */
+PCUT_TEST(stopwatch_emulation_works_small)
+{
+	stopwatch_t sw = STOPWATCH_INITIALIZE_STATIC;
+	stopwatch_set_elapsed(&sw, 42);
+	PCUT_ASSERT_INT_EQUALS(42, (int) stopwatch_get_nanos(&sw));
+}
+
+/* Checks that setting time works for big values too. */
+PCUT_TEST(stopwatch_emulation_works_big)
+{
+	stopwatch_t sw = STOPWATCH_INITIALIZE_STATIC;
+	stopwatch_set_elapsed(&sw, 4200000000021);
+	PCUT_ASSERT_EQUALS(4200000000021, (long long) stopwatch_get_nanos(&sw));
+}
+
+PCUT_EXPORT(perf);