tests/end2end: run each test's SDoc server from its folder, unless specified otherwise

This is a cleaner approach for sandboxing the test environment and its outputs.

The optional cwd= parameter is forward-looking and will be used for testing the Diff screen feature where a custom Git tree setup must be done in a temporary folder.

Author: stanislaw

tests/end2end/server.py

@@ -86,12 +86,16 @@ def __init__(
         config_path: Optional[str] = None,
         port: Optional[int] = None,
         expectations: Optional[List] = None,
+        cwd: Optional[str] = None,
     ):
         is_parallel_execution = test_environment.is_parallel_execution
 
         assert os.path.isdir(input_path)
         if config_path is not None:
-            assert os.path.exists(config_path)
+            assert os.path.exists(config_path), config_path
+        if cwd is not None:
+            assert os.path.isdir(cwd), cwd
+
         self.path_to_tdoc_folder = input_path
         self.output_path: Optional[str] = output_path
         self.config_path: Optional[str] = config_path
@@ -123,6 +127,8 @@ def __init__(
             else ["INFO:     Application startup complete."]
         )
 
+        self.cwd: str = cwd if cwd is not None else input_path
+
         # All of these below become initialized/used starting from run()
         self.process = None
         self.log_file_out = None