--- old/test/hotspot/gtest/runtime/test_os_windows.cpp	2019-09-27 10:20:21.230952400 +0200
+++ new/test/hotspot/gtest/runtime/test_os_windows.cpp	2019-09-27 10:20:20.558950800 +0200
@@ -85,27 +85,29 @@
         << "Failed to allocate memory at requested location " << expected_location << " of size " << expected_allocation_size;
 }
 
-
-// Test which tries to find out if the os::stat, os::open and os::dir_is_empty methods
-// can handle long path names correctly.
+// The types of path modifications we randomly apply to a path. They should not change the file designated by the path.
 enum ModsFilter {
-  Allow_None = 0,
-  Allow_Sep_Mods = 1,
-  Allow_Dot_Path = 2,
-  Allow_Dot_Dot_Path = 4,
+  Allow_None = 0, // No modifications
+  Allow_Sep_Mods = 1, // Replace '\\' by any sequence of '/' or '\\' or at least length 1.
+  Allow_Dot_Path = 2, // Add /. segments at random positions
+  Allow_Dot_Dot_Path = 4, // Add /../<correct-dir> segments at random positions.
   Allow_All = Allow_Sep_Mods | Allow_Dot_Path | Allow_Dot_Dot_Path
 };
 
+// The mode in which to run.
 enum Mode {
-  TEST,
-  EXAMPLES,
-  BENCH
+  TEST, // Runs the test. This is the normal modus.
+  EXAMPLES, // Runs example which document the behaviour of the Windows system calls.
+  BENCH // Runs a small benchmark which tries to show the costs of using the *W variants/_wfullpath.
 };
 
+// Parameters of the test.
 static ModsFilter mods_filter = Allow_All;
-static int mods_per_path = 50;
+static int mods_per_path = 50; // The number of variants of a path we try.
 static Mode mode = TEST;
 
+
+// Utility methods
 static void get_current_dir_w(wchar_t* path, size_t size) {
   DWORD count = GetCurrentDirectoryW((DWORD) size, path);
   EXPECT_GT((int) count, 0) << "Failed to get current directory: " << GetLastError();
@@ -160,10 +162,6 @@
   return err == ERROR_SUCCESS;
 }
 
-static const wchar_t* sep_replacements[] = {
-  L"\\", L"\\/", L"/", L"//", L"\\\\/\\", L"//\\/"
-};
-
 static wchar_t* my_wcscpy_s(wchar_t* dest, size_t size, wchar_t* start, const wchar_t* to_copy) {
   size_t already_used = dest - start;
   size_t len = wcslen(to_copy);
@@ -175,6 +173,12 @@
   return dest + wcslen(to_copy);
 }
 
+// The currently finite list of seperator sequences we might use instead of '\\'.
+static const wchar_t* sep_replacements[] = {
+  L"\\", L"\\/", L"/", L"//", L"\\\\/\\", L"//\\/"
+};
+
+// Takes a path and modifies it in a way that it should still designate the same file.
 static bool unnormalize_path(wchar_t* result, size_t size, bool is_dir, const wchar_t* path) {
   wchar_t* dest = result;
   const wchar_t* src = path;
@@ -312,6 +316,20 @@
 static void check_file(wchar_t* path) {
   check_file_impl(path);
 
+  // Check os::same_files at least somewhat.
+  char buf[JVM_MAXPATHLEN];
+
+  if (convert_to_cstring(buf, JVM_MAXPATHLEN, path)) {
+    wchar_t mod[JVM_MAXPATHLEN];
+
+    if (unnormalize_path(mod, JVM_MAXPATHLEN, false, path)) {
+      char mod_c[JVM_MAXPATHLEN];
+      if (convert_to_cstring(mod_c, JVM_MAXPATHLEN, mod)) {
+        EXPECT_EQ(os::same_files(buf, mod_c), true) << "os::same files failed for \\" << path << "\" and \"" << mod_c << "\"";
+      }
+    }
+  }
+
   for (int i = 0; mods_filter != Allow_None && i < mods_per_path; ++i) {
     wchar_t tmp[JVM_MAXPATHLEN];
     if (unnormalize_path(tmp, JVM_MAXPATHLEN, false, path)) {
@@ -367,6 +385,7 @@
                   succ = true;
                 }
 
+                // Note that we really don't use the full path name, but just add the cost of running _wfullpath.
                 os::free(tmp);
               }
               if (!succ) {
@@ -448,6 +467,8 @@
 #define NAME_PART_50 L"01234567890123456789012345678901234567890123456789"
 #define NAME_PART_250 NAME_PART_50 NAME_PART_50 NAME_PART_50 NAME_PART_50 NAME_PART_50
 
+// Test which tries to find out if the os::stat, os::open and os::dir_is_empty methods
+// can handle long path names correctly.
 TEST_VM(os_windows, handle_long_paths) {
   static wchar_t cwd[JVM_MAXPATHLEN];
   static wchar_t nearly_long_rel_path[JVM_MAXPATHLEN];