Add unit tests.

Author: lntue

libc/test/include/CMakeLists.txt

@@ -484,6 +484,21 @@ add_libc_test(
     libc.include.llvm-libc-macros.math_function_macros
 )
 
+add_libc_test(
+  math_constants_c_test
+  C_TEST
+  UNIT_TEST_ONLY
+  SUITE
+    libc_include_tests
+  SRCS
+    math_constants_test.c
+  COMPILE_OPTIONS
+    -Wall
+    -Werror
+  DEPENDS
+    libc.include.llvm-libc-macros.math_macros
+)
+
 # Test `#include <...>` of each header in each available language mode.
 # This is gated on -DLLVM_LIBC_BUILD_HEADER_TESTS=ON until all the bugs
 # in headers are fixed so the tests all compile.

libc/test/include/math_constants_test.c

@@ -0,0 +1,23 @@
+//===-- Unittests for math constants --------------------------------------===//
+//
+// 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 "include/llvm-libc-macros/math-macros.h"
+
+#define IS_DOUBLE(X) _Generic((X), double: 1, default: 0)
+
+#define IS_FLOAT(X) _Generic((X), float: 1, default: 0)
+
+// check if macro is defined
+#ifndef M_PI
+#error "M_PI macro is not defined"
+#else
+int main(void) {
+  _Static_assert(IS_DOUBLE(M_PI), "M_PI is not of double type.");
+  _Static_assert(IS_FLOAT(M_PIf), "M_PIf is not of float type.");
+  return 0;
+}
+#endif