By analyzing the blame information on this pull request, we identified @mback2k, @yangtse and @dfandrich to be potential reviewers

Why do you want to hardcode the use of cygpath? I am running the testsuite, including OpenSSH tests using CopSSH, using just Msys2 and MinGW-w64 from an Msys2 shell just fine. Even Msys and MinGW32 works just fine. Please see here.

The truth is opposite. Currently path is hardcoded in testsuite as testsuite depends on that any Msys path must starts with "/cygdrive".
The content of /etc/fstab on freshly installed Msys2:

# For a description of the file format, see the Users Guide
# http://cygwin.com/cygwin-ug-net/using.html#mount-table

# DO NOT REMOVE NEXT LINE. It remove cygdrive prefix from path
none / cygdrive binary,posix=0,noacl,user 0 0

Moreover, for example, I mount my development directory as /dvlp root path. More variants is possible.
Currently testsuite can't run on freshly installed Msys2/MinGW64 even with default settings.
cygpath is core Cygwin/Msys program, hardly you can find Msys with default ln, ls, rm, tr, but without cygpath.

I can confirm msys2 /cygdrive/ paths don't work but I can also confirm original mingw32 (mine at least) doesn't come with a cygpath utility. We probably could use a function to transform the path depending on what's available.

@jay, confirming, there are old Msys/MinGW without cygpath.
Developing more flexible patch, will update this PR.

Closing with 20 days with no comments to the review remarks. Feel free to re-open when/if we come back to this work again.

It's not abandoned. I had to learn Perl to write module which is flexible enough to handle all Msys/Cygwin configurations. Will publish it soon, but I can't reopen this PR - only repo owners can do this.

Well, if it is a different fix then it could warrant a new separate pull request. But sure, I'll reopen this if you think it is better.

@Karlson2k I'm curious about the test on 'MSWin32' in runtests.pl. This includes e.g. Strawberry Perl, but the .pl script(s) depends on a working fork which to me seems only Cygwin32/64 Perl has. Have you tried other Perls on Windows? Since I'm a Perl n00b myself, I wonder how runtest.pl could be made to work with Strawberry Perl on Windows.

@gvanem, Strawberry Perl as well as ActivePerl have fork emulation on Windows: http://perldoc.perl.org/perlfork.html
But testsuite depends on other GNU tools and process paths in Unix-style. So test can be run only on Msys/Cygwin environment with Perl build for Msys/Cygwin. But I think that support for native Windows Perl can be added without massive overhauling.

So test can be run only on Msys/Cygwin environment with Perl build for Msys/Cygwin.

Thanks. Just what I thought.

Updated with new Perl helper module.
Thoroughly tested path conversion in any possible combinations under Msys/Msys2/Cygwin.

Updated with improved compatibility with older Perl.

thanks!