diff --git a/tests/Test.h b/tests/Test.h
index 0430c7e5..5d69714e 100644
--- a/tests/Test.h
+++ b/tests/Test.h
@@ -1,4 +1,5 @@
-#pragma once
+#ifndef __TEST_H_
+#define __TEST_H_
 #include <stdbool.h>
 
 int printf(const char*, ...);
@@ -13,15 +14,15 @@ int printf(const char*, ...);
         return true;                                                                                                   \
     } while (0)
 
-#define TEST_FAIL()                                                                                                    \
+#define TEST_FAIL(expr)                                                                                                \
     do {                                                                                                               \
-        printf("no\n");                                                                                                \
+        printf("no (%s)\n", #expr);                                                                                    \
         return false;                                                                                                  \
     } while (0)
 
 #define EXPECT(expr)                                                                                                   \
     do {                                                                                                               \
-        if (!(expr)) { TEST_FAIL(); }                                                                                  \
+        if (!(expr)) { TEST_FAIL(expr); }                                                                              \
     } while (0)
 
 #define EXPECT_EQ(a, b) EXPECT((a) == (b))
@@ -33,4 +34,6 @@ int printf(const char*, ...);
 #define RUN_TEST(name)                                                                                                 \
     do {                                                                                                               \
         if (!test_##name()) return 1;                                                                                  \
-    } while (0)
\ No newline at end of file
+    } while (0)
+
+#endif
\ No newline at end of file
diff --git a/tests/libc/Makefile b/tests/libc/Makefile
index 3f6e9ce5..dc0dd772 100644
--- a/tests/libc/Makefile
+++ b/tests/libc/Makefile
@@ -4,7 +4,7 @@ DESTDIR := $(LUNA_ROOT)/initrd/bin
 build:
 	@mkdir -p $(TESTDIR)/bin
 	$(LUNA_ROOT)/tools/sync-libc.sh
-	$(CC) $(TESTDIR)/string.c $(TESTDIR)/Test.c -I$(LUNA_ROOT)/tests -o $(TESTDIR)/bin/test-libc
+	$(CC) $(TESTDIR)/string.c $(TESTDIR)/Test.c -I$(LUNA_ROOT)/tests -o $(TESTDIR)/bin/test-libc -Wall -Wextra -Wno-stringop-overread -Werror
 
 install:
 	$(LUNA_ROOT)/tools/clean.sh
diff --git a/tests/libc/Test.c b/tests/libc/Test.c
index b97475b0..517c5e9a 100644
--- a/tests/libc/Test.c
+++ b/tests/libc/Test.c
@@ -1,9 +1,11 @@
 #include "Test.h"
 
 DEFINE_TEST(strlen);
+DEFINE_TEST(strnlen);
 
 int main()
 {
     START_TEST_CASE(string.h);
     RUN_TEST(strlen);
+    RUN_TEST(strnlen);
 }
\ No newline at end of file
diff --git a/tests/libc/string.c b/tests/libc/string.c
index a603dcc6..f3d1bf2f 100644
--- a/tests/libc/string.c
+++ b/tests/libc/string.c
@@ -17,5 +17,28 @@ DEFINE_TEST(strlen)
 
     EXPECT_EQ(len, 0);
 
+    TEST_SUCCESS();
+}
+
+DEFINE_TEST(strnlen)
+{
+    START_TEST(strnlen);
+
+    const char* str = "What is going on?";
+
+    size_t len = strnlen(str, 20);
+
+    EXPECT_EQ(len, 17);
+
+    len = strnlen(str, 15);
+
+    EXPECT_EQ(len, 15);
+
+    char buf[] = {'H', 'e', 'l', 'l', 'o'};
+
+    len = strnlen(buf, sizeof(buf));
+
+    EXPECT_EQ(len, sizeof(buf));
+
     TEST_SUCCESS();
 }
\ No newline at end of file