add support for appveyor MacOS VMs for testing

This commit adds code to set up
`shell_connection`-download tests on appeyor's
MacOS workers in such a way that our user-installed
`7z` binary is found.

Author: christian-monch

datalad_next/utils/tests/test_shell_connection.py

@@ -145,6 +145,13 @@ def test_upload(sshserver, tmp_path):
         _check_ls_result(ssh_executor, common_files[0])
 
 
+def _print_env(ssh_executor: ShellCommandExecutor):
+    r = ssh_executor.execute_command(b'uname -a')
+    print(repr(tuple(r)), file=sys.stderr)
+    r = ssh_executor.execute_command(b'env')
+    print(repr(tuple(r)), file=sys.stderr)
+
+
 def test_download(sshserver, tmp_path):
     ssh_url, local_path = sshserver
     ssh_args, ssh_path = _get_cmdline(ssh_url)
@@ -157,12 +164,17 @@ def test_download(sshserver, tmp_path):
         # perform an operation on the remote shell
         _check_ls_result(ssh_executor, common_files[0])
 
+        # The following allows the appveyor Mac VMs to find `7z`-binaries
+        r = ssh_executor.execute_command(
+            b'if [ $(uname) == "Darwin" ]; then export PATH="$PATH":/usr/local/bin; fi')
+        consume(r)
         # download file from server and verify its content
         r, stderr = ssh_executor.download(
             PurePosixPath(ssh_path + '/' + test_file_name),
             download_file)
         if r != 0:
             print('ssh download stderr output:', repr(stderr), file=sys.stderr)
+            _print_env(ssh_executor)
         assert r == 0
         assert download_file.read_text() == content
 
@@ -179,12 +191,17 @@ def test_end_marker_download(sshserver, tmp_path):
     with shell_connection(ssh_args) as ssh_executor:
         server_file.write_bytes(ssh_executor.end_marker)
 
+        # The following allows the appveyor Mac VMs to find `7z`-binaries
+        r = ssh_executor.execute_command(
+            b'if [ $(uname) == "Darwin" ]; then export PATH="$PATH":/usr/local/bin; fi')
+        consume(r)
         # download file from server and verify its content
         r, stderr = ssh_executor.download(
             PurePosixPath(ssh_path + '/' + test_file_name),
             download_file)
         if r != 0:
             print('ssh download stderr output:', repr(stderr), file=sys.stderr)
+            _print_env(ssh_executor)
         assert r == 0
         assert download_file.read_bytes() == ssh_executor.end_marker