feat: add comprehensive unit tests for FragmentClient methods; include shared test constants

tests/001_test_decode.py

@@ -23,6 +23,9 @@ PAYLOADS = [
 ]
 
 
+# Decode valid payload tests
+
+
 @pytest.mark.parametrize("payload", PAYLOADS)
 def test_decode_payload(payload: str) -> None:
     result = clean_decode(payload)
@@ -31,6 +34,9 @@ def test_decode_payload(payload: str) -> None:
     assert all(ord(c) < 128 for c in result), f"non-ASCII chars in {result!r}"
 
 
+# Edge case tests
+
+
 def test_empty_payload_returns_empty_string() -> None:
     assert clean_decode("") == ""