added fail under directory as input unit test

src/ps_test/test_CorePsPlatform.cs

@@ -93,7 +93,7 @@ namespace PSTests
         }
 
         [Fact]
-        public static void TestIsHardLink()
+        public static void TestIsHardLinkWithFileSystemInfo()
         {
             // a file that should exist on every *nix distro
 
@@ -102,7 +102,6 @@ namespace PSTests
             {
                 File.Create(path);
             }
-
             // Create a file to write to using StreamWriter. 
             // convert string to stream.  On Windows, this appears to be handled, but on *nix, we apparently need to convert to UTF8.
             byte[] byteArray    = System.Text.Encoding.UTF8.GetBytes(path);
@@ -119,9 +118,20 @@ namespace PSTests
         }
 
         [Fact]
-        public static void TestIsHardLinkFailsWithDirectory()
+        public static void TestIsHardLinkFailsWithDirectoryWithFileSystemInfo()
         {
-             
+            // A folder that should exist on every *nix system
+            string path = @"/tmp";
+
+            // Create a file to write to using StreamWriter. 
+            // convert string to stream.  On Windows, this appears to be handled, but on *nix, we apparently need to convert to UTF8.
+            byte[] byteArray    = System.Text.Encoding.UTF8.GetBytes(path);
+            MemoryStream stream = new MemoryStream(byteArray);
+
+            // Convert `path` string to FileSystemInfo data type. And now, it should return true
+            FileSystemInfo fd = new FileInfo(path);
+            Assert.False(Platform.NonWindowsIsHardLink(fd));
+
         }
 
     }