Improve swap_link with temp link before removing link.

Update test, now test_swap_link pass.

swap_link.py

@@ -21,12 +21,27 @@ def swap_link(lnk, tgt):
         elif tpath.readlink().resolve() == lnpath.resolve() :
             raise Exception("Target is a link to link to be fixed...")
     
-    try:
-        lnpath.unlink()
-    except Exception(e):
-        raise Exception("Failed to unlink lnk. Check permissions!")
-
-    lnpath = Path(lnk)
+    tmp_suffix = 0
+    tmp_prefix = 'temp'
+    tmp_name = tmp_prefix + str(tmp_suffix)
+    tmp_path = Path(lnpath.parent / tmp_name)
+    while tmp_path.exists() or tmp_path.is_symlink():
+        tmp_suffix += 1
+        tmp_name = tmp_prefix + str(tmp_suffix)
+        tmp_path = Path(lnk.parent / tmp_name)
 
     sym_path = relpath(tgt, lnk)[3:]
-    lnpath.symlink_to(sym_path)
+
+    try:
+        tmp_path.symlink_to(sym_path)
+    except Exception:
+        print(f"Attempted to create tmp link: {tmp_name}")
+        raise Exception("Failed to create new symlink. Check permissions!")
+
+    try:
+        lnpath.unlink()
+    except Exception:
+        tmp_path.unlink()
+        raise Exception("Failed to remove broken link. Check permissions!")
+    
+    tmp_path.rename(lnk)

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())