Index: test/std/numerics/c.math/abs.fail.cpp
===================================================================
--- /dev/null
+++ test/std/numerics/c.math/abs.fail.cpp
@@ -0,0 +1,24 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include <cstdlib>
+
+#include "test_macros.h"
+
+#ifndef _LIBCPP_VERSION
+#error _LIBCPP_VERSION not defined
+#endif
+
+int main()
+{
+    unsigned int ui = -5;
+    abs(ui); // expected-error {{Call to 'abs' is ambiguous}}
+    
+    return 0;
+}
+
Index: test/std/numerics/c.math/abs.pass.cpp
===================================================================
--- /dev/null
+++ test/std/numerics/c.math/abs.pass.cpp
@@ -0,0 +1,52 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include <math.h>
+#include <assert.h>
+
+#include "test_macros.h"
+
+#ifndef _LIBCPP_VERSION
+#error _LIBCPP_VERSION not defined
+#endif
+
+template <class T>
+void test_abs()
+{
+    T val = -5;
+    T pos_val = 5;
+    
+    assert(abs(val) == 5);
+    assert(abs(pos_val) == 5);
+    
+    ASSERT_SAME_TYPE(decltype(abs(val)), T);
+}
+
+void test_big()
+{
+    long long int big_value = 9223372036854775800; // a value to big for ints to store
+    long long int negative_big_value = -big_value;
+    assert(abs(negative_big_value) == big_value); // make sure it doesnt get casted to a smaller type
+}
+
+int main()
+{
+    test_abs<int>();
+    test_abs<long int>();
+    test_abs<long long int>();
+    test_abs<long double>();
+    test_abs<double>();
+    test_abs<float>();
+    test_abs<short int>();
+    test_abs<char>();
+    
+    test_big();
+    
+    return 0;
+}
+