Fixtures for WebDAV based tests

These replace the old `serve_path_via_webdav` approach. This new
approach is more convenient, and has better test isolation.

Demo follows in next commit.

Ping datalad#295

datalad_next/conftest.py

@@ -16,4 +16,8 @@
     dataset,
     #function-scope, Dataset instance with underlying repository
     existing_dataset,
+    # session-scope, standard webdav credential (full dict)
+    webdav_credential,
+    # function-scope, serve a local temp-path via WebDAV
+    webdav_server,
 )

datalad_next/tests/fixtures.py

@@ -8,6 +8,7 @@
 from datalad_next.datasets import Dataset
 from datalad_next.tests.utils import (
     SkipTest,
+    WebDAVPath,
     external_versions,
     get_git_config_global_fpath,
     md5sum,
@@ -202,3 +203,40 @@ def existing_dataset(dataset):
     """
     dataset.create(result_renderer='disabled')
     yield dataset
+
+
+@pytest.fixture(autouse=False, scope="session")
+def webdav_credential():
+    yield dict(
+        name='dltest-my&=webdav',
+        user='datalad',
+        secret='secure',
+        type='user_password',
+    )
+
+
+@pytest.fixture(autouse=False, scope="function")
+def webdav_server(tmp_path_factory, webdav_credential):
+    """Provides a WebDAV server, serving a temporary directory
+
+    The fixtures yields an instance of ``WebDAVPath``, provides the
+    following essential attributes:
+
+    - ``path``: ``Path`` instance of the served temporary directory
+    - ``url``: HTTP URL to access the WebDAV server
+
+    Server access requires HTTP Basic authentication with the credential
+    provided by the ``webdav_credential`` fixture.
+    """
+    auth = (webdav_credential['user'], webdav_credential['secret'])
+    # must use the factory to get a unique path even when a concrete
+    # test also uses `tmp_path`
+    path = tmp_path_factory.mktemp("webdav")
+    # this looks a little awkward, but is done to avoid a change in
+    # WebDAVPath. It would be better to have WebDAVPath directly
+    # set `.url` internally, but that would require adjusting
+    # the old `serve_path_via_webdav`
+    server = WebDAVPath(path, auth=auth)
+    with server as server_url:
+        server.url = server_url
+        yield server