Start adding tests.

test/fixtures/usvfs_global_test/RedFileSystemTest/example.cpp

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+#include <filesystem>
+#include <fstream>
+
+std::filesystem::path storages_path;
+std::filesystem::path hudpainter_path;
+bool has_mo2;
+
+// See below main() for implementation.
+void request_directory(std::filesystem::path);
+std::filesystem::path restrict_path(std::filesystem::path);
+std::vector<std::filesystem::path> get_files();
+std::string read_file(std::filesystem::path);
+void write_file(std::filesystem::path);
+
+// Expected path when not using MO2
+int main()
+{
+  // RedFileSystem plugin (DLL) is loaded.
+  has_mo2 = GetModuleHandle(TEXT("usvfs_x64.dll")) != nullptr;
+
+  // Setup paths
+  auto path      = std::filesystem::absolute(".");    // <GAME>\bin\x64
+  auto game_path = path.parent_path().parent_path();  // <GAME>
+
+  storages_path = game_path / "r6" / "storages";  // <GAME>\r6\storages
+
+  // Create storages directory if it is no present.
+  request_directory(storages_path);  // <GAME>\r6\storages
+
+  // Game is running...
+
+  // HUD Painter request its storage endpoint.
+  hudpainter_path = storages_path / "HUDPainter";
+  request_directory(hudpainter_path);  // <GAME>\r6\storages\HUDPainter
+
+  // HUD Painter request a file (present in archive).
+  auto default_path =
+      restrict_path("DEFAULT.json");  // <GAME>\r6\storages\HUDPainter\DEFAULT.json
+
+  // HUD Painter read file in `default_path` with success.
+  auto data = read_file(default_path);  // <GAME>\r6\storages\HUDPainter\DEFAULT.json
+
+  // HUD Painter request another file.
+  auto test_path =
+      restrict_path("TEST.json");  // <GAME>\r6\storages\HUDPainter\TEST.json
+
+  // (Bug A) HUD Painter write file in `test_path`.
+  write_file(test_path);  // <GAME>\r6\storages\HUDPainter\TEST.json
+                          // file is created with workaround, not created otherwise.
+
+  // (Bug B) HUD Painter request list of files.
+  //         TEST.json is successfully created when using workaround.
+  auto files = get_files();  // [0] <GAME>\r6\storages\HUDPainter\DEFAULT.json
+
+  // files.size() == 1
+
+  // Expect:
+  // files.size() == 2
+  //
+  // [0] <GAME>\r6\storages\HUDPainter\DEFAULT.json
+  // [1] <GAME>\r6\storages\HUDPainter\TEST.json
+}
+
+// Create directory if it is no present
+void request_directory(std::filesystem::path path)
+{
+  bool is_present = std::filesystem::exists(path);
+
+  if (is_present) {
+    return;
+  }
+  std::filesystem::create_directory(path);
+}
+
+// Resolve path for HUDPainter (security layer)
+std::filesystem::path restrict_path(std::filesystem::path path)
+{
+  auto real_path = std::filesystem::weakly_canonical(hudpainter_path / path);
+
+  // Workaround when using MO2
+  if (has_mo2) {
+    return real_path;
+  }
+  // Expected implementation without MO2
+  if (real_path.string().find(hudpainter_path.string() + "\\") != 0) {
+    // "throw" error
+  }
+  return real_path;
+}
+
+// List files in storage of HUDPainter.
+std::vector<std::filesystem::path> get_files()
+{
+  std::vector<std::filesystem::path> files;
+  auto entries = std::filesystem::directory_iterator(hudpainter_path);
+
+  for (const auto& entry : entries) {
+    if (entry.is_regular_file()) {
+      auto file_name = entry.path().filename();
+      auto file_path =
+          hudpainter_path /
+          file_name;  // Culprit of bug B. When using entry.path() directly, it works.
+
+      files.emplace_back(file_path);
+    }
+  }
+  return files;
+}
+
+std::string read_file(std::filesystem::path path)
+{
+  std::ifstream stream;
+
+  // With workaround:
+  // std::filesystem::create_directories(path.parent_path());
+  stream.open(path);
+  if (!stream.is_open()) {
+    return "";
+  }
+  std::stringstream data;
+
+  data << stream.rdbuf();
+  stream.close();
+  return data.str();
+}
+
+void write_file(std::filesystem::path path)
+{
+  std::ofstream stream;
+
+  // With workaround:
+  // std::filesystem::create_directories(path.parent_path());
+  stream.open(path, std::ios_base::trunc);
+  if (!stream.is_open()) {
+    return;
+  }
+  stream << "<DATA>";
+  stream.close();
+}

test/fixtures/usvfs_global_test/RedFileSystemTest/expected/mods/HUD Painter/r6/storages/HUDPainter/DEFAULT.json

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+{
+  "propertiesDefault": [
+    {
+      "name": "MainColors.Red",
+      "red": 1.1761,
+      "green": 0.3809,
+      "blue": 0.3476,
+      "alpha": 1
+    }
+  ]
+}

test/fixtures/usvfs_global_test/RedFileSystemTest/expected/overwrite/r6/storages/HUDPainter/TEST.json

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+{}

test/fixtures/usvfs_global_test/RedFileSystemTest/source/mods/HUD Painter/r6/storages/HUDPainter/DEFAULT.json

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+{
+  "propertiesDefault": [
+    {
+      "name": "MainColors.Red",
+      "red": 1.1761,
+      "green": 0.3809,
+      "blue": 0.3476,
+      "alpha": 1
+    }
+  ]
+}

test/usvfs_global_test/usvfs_global_test.cpp

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+#include <gtest/gtest.h>
+
+#include <filesystem>
+#include <fstream>
+
+class
+{
+  bool initialize(int argc, char* argv[])
+  {
+    // extract the data path
+    if (argc != 2) {
+      std::cerr << "missing data path, aborting\n";
+      return false;
+    }
+    m_data = std::filesystem::path{argv[1]};
+
+    if (!exists(m_data)) {
+      std::cerr << "data path '" << m_data.string() << "'does not exist\n";
+      return false;
+    }
+
+    return true;
+  }
+
+  friend int main(int argc, char* argv[]);
+  std::filesystem::path m_data;
+
+public:
+  const auto& data() const { return m_data; }
+} parameters;
+
+TEST(BasicTest, SimpleTest)
+{
+  const auto data = parameters.data();
+
+  ASSERT_TRUE(exists(data));
+  ASSERT_TRUE(exists(data / "docs"));
+  ASSERT_TRUE(exists(data / "empty"));
+  ASSERT_TRUE(exists(data / "docs" / "doc.txt"));
+  ASSERT_TRUE(exists(data / "readme.txt"));
+}
+
+TEST(RedFileSystemTest, RedFileSystemTest)
+{
+  const auto data = parameters.data();
+
+  const auto storages_path   = data / "r6" / "storages";
+  const auto hudpainter_path = storages_path / "HUDPainter";
+
+  ASSERT_TRUE(exists(hudpainter_path / "DEFAULT.json"));
+
+  {
+    std::ofstream of{hudpainter_path / "TEST.json"};
+    of << "{}\n";
+  }
+
+  // ASSERT_EQ(std::filesystem::path{}, weakly_canonical(hudpainter_path /
+  // "TEST.json"));
+}
+
+int main(int argc, char* argv[])
+{
+  testing::InitGoogleTest(&argc, argv);
+
+  // initialize parameters from remaining arguments
+  if (!parameters.initialize(argc, argv)) {
+    return -1;
+  }
+
+  return RUN_ALL_TESTS();
+}