[libc] Add a test for `fputs` to check using `stdout` and `stderr`

[jhuber6]

Summary

This patch adds a test directly for the fputs function similar to the
existing puts test. This lets us know that the default file pointers
are function and the fputs interface works.

[michaelrj]

This should probably be more similar to the putc test, which writes to a file so that the result can be checked.

[jhuber6]

In D152288#4400153, @michaelrj wrote:

This should probably be more similar to the putc test, which writes to a file so that the result can be checked.

Yeah, I wanted something to test this for the GPU but I don't currently support any FILE IO that's not stderr or stdout. There's some more work on that front required.

libc/test/src/stdio/CMakeLists.txt

add_libc_test(
   SUITE
     libc_stdio_unittests
   SRCS
     puts_test.cpp
   DEPENDS
     libc.src.stdio.puts
 )
 
+add_libc_test(
+  fputs_test
+  SUITE
+    libc_stdio_unittests
+  SRCS
+    fputs_test.cpp
+  DEPENDS
+    libc.src.stdio.fputs
+)
+
 add_libc_unittest(
   putc_test
   SUITE
     libc_stdio_unittests
   SRCS
     putc_test.cpp
   DEPENDS
     libc.src.stdio.putc

libc/test/src/stdio/fputs_test.cpp

+//===-- Unittests for puts ---------------------------------------------===//
+//
+// 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 "src/__support/File/file.h"
+#include "src/stdio/fputs.h"
+
+#include "test/UnitTest/Test.h"
+
+TEST(LlvmLibcPutsTest, PrintOut) {
+  int result;
+
+  constexpr char simple[] = "A simple string written to stdout\n";
+  result =
+      __llvm_libc::fputs(simple, reinterpret_cast<FILE *>(__llvm_libc::stdout));
+  EXPECT_GE(result, 0);
+
+  constexpr char more[] = "A simple string written to stderr\n";
+  result =
+      __llvm_libc::fputs(more, reinterpret_cast<FILE *>(__llvm_libc::stderr));
+  EXPECT_GE(result, 0);
+}