diff --git a/tests/lib/libc/test_memcmp.cpp b/tests/lib/libc/test_memcmp.cpp
index b4eb293..c644bec 100644
--- a/tests/lib/libc/test_memcmp.cpp
+++ b/tests/lib/libc/test_memcmp.cpp
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2019, Arm Limited. All rights reserved.
+ * Copyright (c) 2019-2020, Arm Limited. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -9,10 +9,54 @@
 #include "lib/libc/string.h"
 }
 
-TEST_GROUP(memcmp) {
+#define BUFFER_SIZE	(16)
 
+TEST_GROUP(memcmp) {
+	TEST_SETUP() {
+		for (int i = 0; i < BUFFER_SIZE; i++) {
+			buffer1[i] = 0;
+			buffer2[i] = 0;
+		}
+	}
+
+	uint8_t buffer1[BUFFER_SIZE];
+	uint8_t buffer2[BUFFER_SIZE];
 };
 
-TEST(memcmp, empty) {
-	LONGS_EQUAL(0, memcmp(NULL, NULL, 0))
+TEST(memcmp, zero_length) {
+	LONGS_EQUAL(0, memcmp(buffer1, buffer2, 0));
+}
+
+TEST(memcmp, same) {
+	LONGS_EQUAL(0, memcmp(buffer1, buffer2, sizeof(buffer1)));
+}
+
+TEST(memcmp, first_diff_positive) {
+	buffer1[0] = 1;
+	LONGS_EQUAL(1, memcmp(buffer1, buffer2, sizeof(buffer1)));
+}
+
+TEST(memcmp, first_diff_negative) {
+	buffer2[0] = 1;
+	LONGS_EQUAL(-1, memcmp(buffer1, buffer2, sizeof(buffer1)));
+}
+
+TEST(memcmp, second_diff_positive) {
+	buffer1[1] = 1;
+	LONGS_EQUAL(1, memcmp(buffer1, buffer2, sizeof(buffer1)));
+}
+
+TEST(memcmp, second_diff_negative) {
+	buffer2[1] = 1;
+	LONGS_EQUAL(-1, memcmp(buffer1, buffer2, sizeof(buffer1)));
+}
+
+TEST(memcmp, last_diff_positive) {
+	buffer1[sizeof(buffer1) - 1] = 1;
+	LONGS_EQUAL(1, memcmp(buffer1, buffer2, sizeof(buffer1)));
+}
+
+TEST(memcmp, last_diff_negative) {
+	buffer2[sizeof(buffer2) - 1] = 1;
+	LONGS_EQUAL(-1, memcmp(buffer1, buffer2, sizeof(buffer1)));
 }