Implement basic version of ssh shell

Signed-off-by: Vladimir Domnich <v.domnich@yadro.com>

tests/helpers.py

@@ -1,9 +1,30 @@
 import traceback
 
+from shell.interfaces import CommandResult
+
 
 def format_error_details(error: Exception) -> str:
-    return "".join(traceback.format_exception(
+    """
+    Converts specified exception instance into a string that includes error message
+    and full stack trace.
+
+    :param Exception error: exception to convert.
+    :return: string containing exception details.
+    """
+    detail_lines = traceback.format_exception(
         etype=type(error),
         value=error,
-        tb=error.__traceback__)
+        tb=error.__traceback__,
     )
+    return "".join(detail_lines)
+
+
+def get_output_lines(result: CommandResult) -> list[str]:
+    """
+    Converts output of specified command result into separate lines trimmed from whitespaces.
+    Empty lines are excluded.
+
+    :param CommandResult result: result which output should be converted.
+    :return: list of lines extracted from the output.
+    """
+    return [line.strip() for line in result.stdout.split("\n") if line.strip()]