[lldb] make the code prettier in FindFileTest.cpp

[xujuntwt95329]

Thanks to @teemperor's comments in https://reviews.llvm.org/D112439

lldb/unittests/Target/FindFileTest.cpp

 //===-- FindFileTest.cpp -------------------------------------------------===//
 //
 // 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 "TestingSupport/SubsystemRAII.h"
 #include "TestingSupport/TestUtilities.h"
 #include "lldb/Host/FileSystem.h"
 #include "lldb/Host/HostInfo.h"
 #include "lldb/Target/PathMappingList.h"
 #include "lldb/Utility/FileSpec.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/FileUtilities.h"
 #include "gtest/gtest.h"
 #include <utility>
 
 using namespace llvm;
 using namespace llvm::sys::fs;
 using namespace lldb_private;
 
 namespace {
 struct Matches {
   FileSpec original;
-  llvm::StringRef remapped;
-  Matches(const char *o, const char *r) : original(o), remapped(r) {}
-  Matches(const char *o, llvm::sys::path::Style style, const char *r)
+  std::string remapped;
+  Matches(llvm::StringRef o, llvm::sys::path::Style style, llvm::StringRef r)
       : original(o, style), remapped(r) {}
 };
 
 class FindFileTest : public testing::Test {
-public:
-  void SetUp() override {
-    FileSystem::Initialize();
-    HostInfo::Initialize();
-  }
-  void TearDown() override {
-    HostInfo::Terminate();
-    FileSystem::Terminate();
-  }
+  SubsystemRAII<FileSystem, HostInfo> subsystems;
 };
 } // namespace
 
 static void TestFileFindings(const PathMappingList &map,
                              llvm::ArrayRef<Matches> matches,
                              llvm::ArrayRef<FileSpec> fails) {
   for (const auto &fail : fails) {
     SCOPED_TRACE(fail.GetCString());
     EXPECT_FALSE(map.FindFile(fail));
   }
 
   for (const auto &match : matches) {
     SCOPED_TRACE(match.original.GetPath() + " -> " + match.remapped);
-    llvm::Optional<FileSpec> remapped;
+    llvm::Optional<FileSpec> remapped = map.FindFile(match.original);
 
-    EXPECT_TRUE(bool(remapped = map.FindFile(match.original)));
-    EXPECT_TRUE(FileSpec(remapped.getValue()).GetPath() ==
-                ConstString(match.remapped).GetStringRef());
+    EXPECT_TRUE(remapped);
+    EXPECT_EQ(FileSpec(remapped.getValue()).GetPath(),
   }
 }
 
 TEST_F(FindFileTest, FindFileTests) {
   const auto *Info = testing::UnitTest::GetInstance()->current_test_info();
   llvm::SmallString<128> DirName, FileName;
   int fd;