Improve swap_link with temp link before removing link.

Update test, now test_swap_link pass.

test/test_swap_link.py

@@ -1,4 +1,6 @@
 import unittest
+from pathlib import Path
+from swap_link import swap_link
 
 class TestSwapLink(unittest.TestCase):
     
@@ -14,7 +16,13 @@ class TestSwapLink(unittest.TestCase):
         # TODO: no writing permission on file
     
     def test_wrong_tgt_file(self):
-        # TODO: non-existing target
+        with self.assertRaises(Exception):
+            swap_link(data_dir+"lnk_dir/tgt_file.txt", data_dir+"inexistent")
         # TODO: target is link to lnk file (can't have 2 symlinks pointing at one another)
-        True
 
+    def test_fix_link(self):
+        lnk = 'test/data/lnk_dir/tgt_file.txt'
+        tgt = 'test/data/tgt_dir/tgt_file.txt'
+        swap_link(lnk, tgt)
+        print(f"Lnk path resolve:")
+        self.assertEqual(Path(lnk).resolve(), Path(tgt).resolve())