Add test for succesful repeated "import" (clone and pull) from git

Diagnose #138 which occurred on Windows.  (A lock for the git pack
file is often held by a previous clone/pull and not released, so the
next pull fails (`PermissionError`).)

test/github/github_importer_spec.py

@@ -0,0 +1,26 @@
+from unittest.mock import MagicMock, patch
+
+from mamba import describe, it, context
+from expects import expect, equal
+
+from pathlib import Path
+
+from crowd_anki.github.github_importer import GitImporter
+
+GitImporter.get_repo_local_path = lambda self, x: Path("/tmp/foo/bar/")
+
+with describe(GitImporter) as self:
+    with context("user is trying to import a deck from a git repo multiple times"):
+        # See #138!
+        with it("should clone the git repo without crashing"):
+            collection_mock = MagicMock()
+            subject = GitImporter(collection_mock)
+            with patch("crowd_anki.github.github_importer.AnkiJsonImporter") as mock_json_importer:
+                subject.clone_repository_and_import("https://github.com/aplaice/colemak_keyboard_layout_dynamic")
+                subject.clone_repository_and_import("https://github.com/aplaice/colemak_keyboard_layout_dynamic")
+                subject.clone_repository_and_import("https://github.com/aplaice/colemak_keyboard_layout_dynamic")
+                expect(mock_json_importer.import_deck_from_path.call_count).to(equal(3))
+
+            # Note: the import itself isn't being tested (we're not,
+            # yet (as of 2021-11) testing import itself in any
+            # situation)!