Require compression program, should fix failing tests on windows

patoolib/__init__.py

@@ -488,8 +488,13 @@ def program_supports_compression(program, exe, compression):
         # * tar programs allow long option --<compression> for supported compressions
         # This way running "tar --<compression> --help" determines, if the compression is supported
         cmd = [exe, f"--{compression}", "--help"]
-        retcode = util.run(cmd, stderr=subprocess.DEVNULL, verbosity=-1)
-        return retcode == 0
+        if util.run(cmd, stderr=subprocess.DEVNULL, verbosity=-1) != 0:
+            # compression is not supported by this tar implementation
+            return False
+        # in addition to the commandline option, tar also needs the corresponding compression program
+        if util.find_program(compression):
+            # the compression program is available for tar
+            return True
     elif program in ('py_tarfile',):
         # the python tarfile module has a fixed list of supported compression modules
         return compression in ('gzip', 'bzip2', 'lzma', 'xz')