tests/httpserver_testcase.py: Add common base class for HTTP tests

Add a common base class for HTTP tests using pytest_httpserver:
- tests/test_httpaccessor.py   (self-contained HTTP test for xcp.accessor)
- tests/test_httprepository.py (self-contained HTTP test for xcp.repository)

Signed-off-by: Bernhard Kaindl <bernhard.kaindl@cloud.com>

Author: bernhardkaindl

stubs/werkzeug/wrappers.pyi

@@ -1,2 +1,3 @@
-from _typeshed import Incomplete
+from _typeshed import Incomplete  # pylint: disable=import-error,no-name-in-module
+Request = Incomplete
 Response = Incomplete

tests/httpserver_testcase.py

@@ -0,0 +1,49 @@
+import os
+import unittest
+from typing import Callable, Optional
+
+import pytest
+
+# Skip the tests in this module if Python <= 3.6 (pytest_httpserver requires Python >= 3.7):
+try:
+    from http.client import HTTPResponse
+
+    from pytest_httpserver import HTTPServer
+    from werkzeug.wrappers import Request, Response
+
+    ErrorHandler = Optional[Callable[[Request], Response]]
+except ImportError:
+    pytest.skip(allow_module_level=True)
+
+
+class HTTPServerTestCase(unittest.TestCase):
+    HTTPResponse = HTTPResponse  # pyright: ignore[reportUnboundVariable]
+    httpserver = HTTPServer()  # pyright: ignore[reportUnboundVariable]
+
+    @classmethod
+    def setUpClass(cls):
+        cls.httpserver.start()
+
+    @classmethod
+    def tearDownClass(cls):
+        cls.httpserver.check_assertions()
+        cls.httpserver.stop()
+
+    @classmethod
+    def serve_file(cls, root, file_path, error_handler=None, real_path=None):
+        # type:(str, str, Optional[Callable[[Request], Response]], Optional[str]) -> None
+        """Expect a GET request and handle it using the local pytest_httpserver.HTTPServer"""
+
+        def handle_get(request):
+            # type:(Request) -> Response
+            """Handle a GET request for the local pytest_httpserver.HTTPServer fixture"""
+            if error_handler:
+                response = error_handler(request)
+                if response:
+                    return response
+            filepath = root + (real_path or file_path)
+            assert os.path.exists(path=filepath)
+            with open(file=filepath, mode="rb") as local_testdata_file:
+                return Response(local_testdata_file.read())
+
+        cls.httpserver.expect_request(uri="/" + file_path).respond_with_handler(func=handle_get)