bpo-37876: Tests for ROT-13 codec (GH-15314)


The Rot-13 codec is for educational use but does not have unit tests,
dragging down test coverage. This adds a few very simple tests.
(cherry picked from commit b3b48c81f09d1472010937f1331c5a208a2a2d48)

Co-authored-by: Zeth <theology@gmail.com>
2 files changed