Added test cases to join.py (TheAlgorithms#10629)

* Added test cases to join.py

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Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: its-100rabh

strings/join.py

@@ -1,10 +1,21 @@
 """
-Program to join a list of strings with a given separator
+Program to join a list of strings with a separator
 """
 
 
 def join(separator: str, separated: list[str]) -> str:
     """
+    Joins a list of strings using a separator
+    and returns the result.
+
+    :param separator: Separator to be used
+                for joining the strings.
+    :param separated: List of strings to be joined.
+
+    :return: Joined string with the specified separator.
+
+    Examples:
+
     >>> join("", ["a", "b", "c", "d"])
     'abcd'
     >>> join("#", ["a", "b", "c", "d"])
@@ -13,16 +24,27 @@ def join(separator: str, separated: list[str]) -> str:
     'a'
     >>> join(" ", ["You", "are", "amazing!"])
     'You are amazing!'
+
+    This example should raise an
+    exception for non-string elements:
     >>> join("#", ["a", "b", "c", 1])
     Traceback (most recent call last):
         ...
-    Exception: join() accepts only strings to be joined
+    Exception: join() accepts only strings
+
+    Additional test case with a different separator:
+    >>> join("-", ["apple", "banana", "cherry"])
+    'apple-banana-cherry'
     """
+
     joined = ""
     for word_or_phrase in separated:
         if not isinstance(word_or_phrase, str):
-            raise Exception("join() accepts only strings to be joined")
+            raise Exception("join() accepts only strings")
         joined += word_or_phrase + separator
+
+    # Remove the trailing separator
+    # by stripping it from the result
     return joined.strip(separator)