test-check-code: prevent from adding Python modules shadowed by ancient C

tests/test-check-code.t

@@ -51,3 +51,15 b' Prevent adding new files in the root dir'
   hgeditor
   hgweb.cgi
   setup.py
+
+Prevent adding modules which could be shadowed by ancient .so/.dylib.
+
+  $ testrepohg files \
+  > mercurial/base85.py \
+  > mercurial/bdiff.py \
+  > mercurial/diffhelpers.py \
+  > mercurial/mpatch.py \
+  > mercurial/osutil.py \
+  > mercurial/parsers.py \
+  > mercurial/zstd.py
+  [1]