[wpiutil] Add compile-time string utilities (ct_string) (#5462)

wpiutil/src/test/native/cpp/ct_string_test.cpp

@@ -0,0 +1,38 @@
+// Copyright (c) FIRST and other WPILib contributors.
+// Open Source Software; you can modify and/or share it under the terms of
+// the WPILib BSD license file in the root directory of this project.
+
+#include "wpi/ct_string.h"  // NOLINT(build/include_order)
+
+#include <string>
+#include <string_view>
+
+#include "gtest/gtest.h"  // NOLINT(build/include_order)
+
+TEST(CtStringTest, Concat) {
+  using namespace wpi::literals;
+  constexpr std::string_view astring = "name";
+  constexpr int arrsize = 5;
+  constexpr auto str = Concat(
+      wpi::ct_string<char, std::char_traits<char>, astring.size()>{astring},
+      "["_ct_string, wpi::NumToCtString<arrsize>(), "]"_ct_string);
+  static_assert(str.size() == 7);
+  ASSERT_EQ(std::string{str}, "name[5]");
+}
+
+TEST(CtStringTest, OperatorPlus) {
+  using namespace wpi::literals;
+  constexpr std::string_view astring = "name";
+  constexpr auto str =
+      wpi::ct_string<char, std::char_traits<char>, astring.size()>{astring} +
+      "[]"_ct_string;
+  static_assert(str.size() == 6);
+  ASSERT_EQ(std::string{str}, "name[]");
+}
+
+TEST(CtStringTest, StringViewConversion) {
+  using namespace wpi::literals;
+  constexpr auto str = "[]"_ct_string;
+  std::string_view sv = str;
+  ASSERT_EQ(sv, "[]");
+}