Closes #12

tests/README.md

@@ -47,6 +47,9 @@ found; insufficient payloads are checked through signal validity.
 Parser tests cover standard and extended CAN IDs, whitespace, payload storage
 boundaries, missing fields, malformed and overflowing numbers, reserved ID bits,
 error paths and line numbers, and integration with signals and comments.
+Duplicate definitions are rejected at their source lines, including equivalent
+extended ID encodings and repeated signal names within a frame. Standard and
+extended frames may share a numeric ID, and separate frames may reuse signal names.
 Signal tests cover complete syntax and numeric validation, scientific notation,
 finite physical parameters and ordered ranges, spaces and tabs, receiver lists,
 unsupported multiplexing, and Intel/Motorola declared-payload boundaries.