diff --git a/test/unit-test/sigv4_utest.c b/test/unit-test/sigv4_utest.c
new file mode 100644
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+++ b/test/unit-test/sigv4_utest.c
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+/*
+ * SigV4 Utility Library v1.0.0
+ * Copyright (C) 2020 Amazon.com, Inc. or its affiliates.  All Rights Reserved.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to
+ * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
+ * the Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+ * IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, 6ING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+#include <string.h>
+
+#include "unity.h"
+
+/* Include paths for public enums, structures, and macros. */
+#include "sigv4_config.h"
+#include "sigv4.h"
+#include "sigv4_internal.h"
+
+/* Default size for output date buffer. */
+#define SIGV4_TEST_BUFFER_SIZE          ( 17 )
+
+/* Size of larger-than-required output date buffer. */
+#define SIGV4_TEST_BUFFER_SIZE_LONG     ( 30 )
+
+/* Size of an output date buffer of insufficient length. */
+#define SIGV4_TEST_BUFFER_SIZE_SHORT    ( 16 )
+
+/* Test valid date inputs. */
+static const char pTestDate[] = "2018-01-18T09:18:06Z";
+static const char pTestLongDate[] = "2018-01-18T09:18:06Z00:00";
+static const char pTestExpected[] = "20180118T091806Z";
+
+/* Test invalid date inputs. */
+static const char pTestShortDate[] = "2018-01T09:18Z";
+static const char pTestInvalidFormat[] = "2018-01-18TT09:18:06Z";
+
+/* File-scoped global variables */
+static SigV4Status_t retCode = SigV4Success;
+static char testBuffer[ SIGV4_TEST_BUFFER_SIZE ] = { 0 };
+static char testBufferLong[ SIGV4_TEST_BUFFER_SIZE_LONG ] = { 0 };
+static char testBufferShort[ SIGV4_TEST_BUFFER_SIZE_SHORT ] = { 0 };
+
+
+/* ============================ UNITY FIXTURES ============================== */
+/* Called before each test method. */
+void setUp()
+{
+}
+
+/* Called after each test method. */
+void tearDown()
+{
+    retCode = SigV4Success;
+    memset( &testBuffer, 0, sizeof( testBuffer ) );
+    memset( &testBufferLong, 0, sizeof( testBufferLong ) );
+    memset( &testBufferShort, 0, sizeof( testBufferShort ) );
+}
+
+/* Called at the beginning of the whole suite. */
+void suiteSetUp()
+{
+}
+
+/* Called at the end of the whole suite. */
+int suiteTearDown( int numFailures )
+{
+    return numFailures;
+}
+/* ==================== Testing SigV4_AwsIotDateToIso8601 =================== */
+
+/**
+ * @brief Test the happy path with zero-initialized and adequately sized output
+ * buffers.
+ */
+void test_SigV4_AwsIotDateToIso8601_Happy_Path()
+{
+    SigV4Status_t returnVal = SigV4Success;
+
+    returnVal = SigV4_AwsIotDateToIso8601( pTestDate, sizeof( pTestDate ), testBuffer, SIGV4_TEST_BUFFER_SIZE );
+
+    TEST_ASSERT_EQUAL( SigV4Success, returnVal );
+    TEST_ASSERT_EQUAL_STRING( pTestExpected, testBuffer );
+
+    returnVal = SigV4_AwsIotDateToIso8601( pTestLongDate, sizeof( pTestLongDate ), testBuffer, SIGV4_TEST_BUFFER_SIZE );
+
+    TEST_ASSERT_EQUAL( SigV4Success, returnVal );
+    TEST_ASSERT_EQUAL_STRING( pTestExpected, testBuffer );
+}
+
+/**
+ * @brief Test NULL and invalid parameters, following order of else-if blocks in
+ * SigV4_AwsIotDateToIso8601().
+ */
+void test_SigV4_AwsIotDateToIso8601_Invalid_Params()
+{
+    SigV4Status_t returnVal = SigV4Success;
+
+    /* Test pDate == NULL */
+    returnVal = SigV4_AwsIotDateToIso8601( NULL, 0, testBuffer, SIGV4_TEST_BUFFER_SIZE );
+    TEST_ASSERT_EQUAL( SigV4InvalidParameter, returnVal );
+
+    /* Test pDateISO8601 == NULL */
+    returnVal = SigV4_AwsIotDateToIso8601( pTestDate, sizeof( pTestDate ), NULL, SIGV4_TEST_BUFFER_SIZE );
+    TEST_ASSERT_EQUAL( SigV4InvalidParameter, returnVal );
+
+    /* Test dateLen < SIGV4_EXPECTED_AWS_IOT_DATE_LEN */
+    returnVal = SigV4_AwsIotDateToIso8601( pTestShortDate, sizeof( pTestShortDate ), testBuffer, SIGV4_TEST_BUFFER_SIZE );
+    TEST_ASSERT_EQUAL( SigV4InvalidParameter, returnVal );
+
+    /* Test dateISO8601Len < SIGV4_ISO_STRING_LEN + 1 */
+    returnVal = SigV4_AwsIotDateToIso8601( pTestDate, sizeof( pTestDate ), testBufferShort, SIGV4_TEST_BUFFER_SIZE_SHORT );
+    TEST_ASSERT_EQUAL( SigV4InvalidParameter, returnVal );
+}
+
+/**
+ * @brief Test invalid input date formats.
+ */
+void test_SigV4_AwsIotDateToIso8601_Invalid_Format()
+{
+    SigV4Status_t returnVal = SigV4Success;
+
+    /* sscanf() failure. */
+    returnVal = SigV4_AwsIotDateToIso8601( pTestInvalidFormat, sizeof( pTestInvalidFormat ), testBuffer, SIGV4_TEST_BUFFER_SIZE );
+    TEST_ASSERT_EQUAL( SigV4ISOFormattingError, returnVal );
+}