Add missing unit tests for GitMergeHandler

Co-authored-by: balajirajput96 <124477404+balajirajput96@users.noreply.github.com>

Author: Copilot

jupyterlab_git/tests/test_handlers.py

@@ -1089,3 +1089,52 @@ async def test_content_getcontent_deleted_file(mock_execute, jp_fetch, jp_root_d
     assert response.code == 200
     payload = json.loads(response.body)
     assert payload["content"] == ""
+
+
+@patch("jupyterlab_git.handlers.GitMergeHandler.git", spec=Git)
+async def test_merge_handler_success(mock_git, jp_fetch, jp_root_dir):
+    # Given
+    local_path = jp_root_dir / "test_path"
+    branch_to_merge = "feature-branch"
+    merge_result = {
+        "code": 0,
+        "message": "Merge made by the 'ort' strategy."
+    }
+    mock_git.merge.return_value = maybe_future(merge_result)
+
+    # When
+    body = {"branch": branch_to_merge}
+    response = await jp_fetch(
+        NAMESPACE, local_path.name, "merge", body=json.dumps(body), method="POST"
+    )
+
+    # Then
+    mock_git.merge.assert_called_with(branch_to_merge, str(local_path))
+    assert response.code == 200
+    payload = json.loads(response.body)
+    assert payload == merge_result
+
+
+@patch("jupyterlab_git.handlers.GitMergeHandler.git", spec=Git)
+async def test_merge_handler_conflict(mock_git, jp_fetch, jp_root_dir):
+    # Given
+    local_path = jp_root_dir / "test_path"
+    branch_to_merge = "conflicting-branch"
+    merge_result = {
+        "code": 1,
+        "command": "git merge conflicting-branch",
+        "message": "Automatic merge failed; fix conflicts and then commit the result."
+    }
+    mock_git.merge.return_value = maybe_future(merge_result)
+
+    # When
+    body = {"branch": branch_to_merge}
+    response = await jp_fetch(
+        NAMESPACE, local_path.name, "merge", body=json.dumps(body), method="POST"
+    )
+
+    # Then
+    mock_git.merge.assert_called_with(branch_to_merge, str(local_path))
+    assert response.code == 500
+    payload = json.loads(response.body)
+    assert payload == merge_result