tests: quote $PYTHON for Windows When unquoted, MSYS sees the colon between the drive letter and path as a Unix path separator and unhelpfully splits on it, feeding only the drive letter as the command. Much chaos ensues. I vaguely remember trying to get the test runner to use /letter/path/to/exe syntax the last time this happened, without success. I doubt a check-code rule would work, since sometimes it is quoted, and sometimes the quotes are escaped.

--- a/tests/test-http-branchmap.t	Mon Jun 26 15:28:28 2017 -0700
+++ b/tests/test-http-branchmap.t	Fri Jul 07 01:05:20 2017 -0400
@@ -87,7 +87,7 @@
   > EOF
   $ echo baz >> b/foo
   $ hg -R b ci -m baz
-  $ hg push -R b -e '$PYTHON oldhg' ssh://dummy/ --encoding latin1
+  $ hg push -R b -e "\"$PYTHON\" oldhg" ssh://dummy/ --encoding latin1
   pushing to ssh://dummy/
   searching for changes
   remote: adding changesets