extended the test for the filewatcher

tests/test_file_watcher.cpp

@@ -1,37 +1,57 @@
 #include "FileWatcher.h"
+#include <cassert>
 #include <cstring>
 #include <filesystem>
+#include <fstream>
+#include <functional>
+#include <future>
 #include <iostream>
 #include <string>
+#include <thread>
 
 int main(int argc, char *argv[]) {
-  FileWatcher fw(
-      std::filesystem::path("/sys/class/backlight/intel_backlight/brightness"));
-
-  file_watch_error started = fw.startWatching();
-
-  if (started == file_watch_error::success) {
-    std::cout << "Started successfully" << std::endl;
-  } else {
-    std::cout << "Error occured!" << std::endl;
-    switch (started) {
-    case file_watch_error::error_unknown:
-      std::cout << "Unknown Error" << std::endl;
-      break;
-    case file_watch_error::error_still_watching:
-      std::cout << "Already watching" << std::endl;
-      break;
-    default:
-      std::cout << "Errno: " << strerror((int)started) << std::endl;
+  {
+    std::ofstream test_file("test");
+    FileWatcher fw(std::filesystem::path("test"));
+    assert(test_file.is_open());
+
+    file_watch_error started = fw.startWatching();
+
+    if (started == file_watch_error::success) {
+      std::cout << "Started successfully" << std::endl;
+    } else {
+      std::cout << "Error occured!" << std::endl;
+      switch (started) {
+      case file_watch_error::error_unknown:
+        std::cout << "Unknown Error" << std::endl;
+        break;
+      case file_watch_error::error_still_watching:
+        std::cout << "Already watching" << std::endl;
+        break;
+      default:
+        std::cout << "Errno: " << strerror((int)started) << std::endl;
+      }
+      return -1;
     }
-    return -1;
-  }
+    auto fw_wait_and_get = std::bind(&FileWatcher::waitAndGet, &fw);
+    auto file_change_output = std::async(std::launch::async, fw_wait_and_get);
 
-  while (true) {
-    std::optional<std::string> st = fw.waitAndGet();
-    std::cout << "Got '" << st.value_or("Nothing") << "' from FileWatcher"
-              << std::endl;
-  }
+    std::string test_string = "hilarious text";
+
+    test_file << test_string;
 
+    test_file.close();
+
+    std::future_status status = file_change_output.wait_for(
+        std::chrono::duration(std::chrono::milliseconds(500)));
+
+    assert(status == std::future_status::ready);
+
+    std::optional<std::basic_string<char>> test_return =
+        file_change_output.get();
+    assert(test_return.has_value());
+    assert(test_return.value() == test_string);
+  }
+  std::cout << "Success!" << std::endl;
   return 0;
 }