Added edit_distance test cases (TheAlgorithms#12984)

* Added edit_distance test cases

* Update edit_distance.py

---------

Co-authored-by: Maxim Smolskiy <mithridatus@mail.ru>

Author: kathrynpete

strings/edit_distance.py

@@ -14,6 +14,20 @@ def edit_distance(source: str, target: str) -> int:
 
     >>> edit_distance("GATTIC", "GALTIC")
     1
+    >>> edit_distance("NUM3", "HUM2")
+    2
+    >>> edit_distance("cap", "CAP")
+    3
+    >>> edit_distance("Cat", "")
+    3
+    >>> edit_distance("cat", "cat")
+    0
+    >>> edit_distance("", "123456789")
+    9
+    >>> edit_distance("Be@uty", "Beautyyyy!")
+    5
+    >>> edit_distance("lstring", "lsstring")
+    1
     """
     if len(source) == 0:
         return len(target)