Reject multi-character split separators

strings/split.py

@@ -17,8 +17,16 @@ def split(string: str, separator: str = " ") -> list:
 
     >>> split(";abbb;;c;", separator=';')
     ['', 'abbb', '', 'c', '']
+
+    >>> split("a--b--c", separator="--")
+    Traceback (most recent call last):
+        ...
+    ValueError: separator must be a single character
     """
 
+    if len(separator) != 1:
+        raise ValueError("separator must be a single character")
+
     split_words = []
 
     last_index = 0

tests/test_split.py

@@ -0,0 +1,12 @@
+import pytest
+
+from strings.split import split
+
+
+def test_split_rejects_multi_character_separator():
+    with pytest.raises(ValueError, match="separator must be a single character"):
+        split("a--b--c", separator="--")
+
+
+def test_split_supports_single_character_separator():
+    assert split("a--b--c", separator="-") == ["a", "", "b", "", "c"]