Report a missing nnunetv2 as an optional dependency in nnUNetV2Runner

`nnUNetV2Runner.__init__` imports `nnunetv2.configuration` directly, so
constructing the runner without nnunetv2 installed raises a bare
ModuleNotFoundError rather than MONAI's OptionalImportError. The dataset
lookup just above it is wrapped in a broad `except Exception`, which
swallows that same ImportError first and logs

    Dataset with name/ID: 123 cannot be found in the record. ...
    please check your input_config.

so the reported cause is the user's configuration, not the missing
package.

Decorate the class with `@require_pkg(pkg_name="nnunetv2")`, as is done
for other optional dependencies (ITKReader, NibabelReader, ...). The
failure now names the package and links the installation docs, and the
misleading dataset warning is no longer emitted.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Signed-off-by: Kirscher <tristan.kirscher@gmail.com>

Author: Kirscher

monai/apps/nnunet/nnunetv2_runner.py

@@ -23,7 +23,7 @@
 from monai.apps.nnunet.utils import NNUNETMode as M
 from monai.apps.nnunet.utils import analyze_data, create_new_data_copy, create_new_dataset_json
 from monai.bundle import ConfigParser
-from monai.utils import ensure_tuple, optional_import
+from monai.utils import ensure_tuple, optional_import, require_pkg
 from monai.utils.misc import run_cmd
 
 load_pickle, _ = optional_import("batchgenerators.utilities.file_and_folder_operations", name="load_pickle")
@@ -38,6 +38,7 @@
 DATASET_ID_FORMAT = r"Dataset[0-9]{3}|[0-9]+"  # regex format for a valid nnUnet dataset name
 
 
+@require_pkg(pkg_name="nnunetv2")
 class nnUNetV2Runner:  # noqa: N801
     """
     ``nnUNetV2Runner`` provides an interface in MONAI to use `nnU-Net` V2 library to analyze, train, and evaluate

tests/apps/nnunet/test_nnunetv2_runner_optional_import.py

@@ -0,0 +1,58 @@
+# Copyright (c) MONAI Consortium
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#     http://www.apache.org/licenses/LICENSE-2.0
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from __future__ import annotations
+
+import os
+import tempfile
+import unittest
+from unittest import mock
+
+from monai.apps.nnunet.nnunetv2_runner import nnUNetV2Runner
+from monai.utils import OptionalImportError
+
+
+class TestnnUNetV2RunnerOptionalImport(unittest.TestCase):
+    """``nnUNetV2Runner`` requires the optional ``nnunetv2`` package to be installed."""
+
+    def setUp(self) -> None:
+        self.test_dir = tempfile.TemporaryDirectory()
+        test_path = self.test_dir.name
+        self.input_config = {
+            "dataset_name_or_id": "123",
+            "dataroot": os.path.join(test_path, "data"),
+            "datalist": os.path.join(test_path, "lists", "task4.json"),
+            "work_dir": os.path.join(test_path, "work"),
+            "nnunet_raw": os.path.join(test_path, "nnUNet_raw"),
+            "nnunet_preprocessed": os.path.join(test_path, "nnUNet_preprocessed"),
+            "nnunet_results": os.path.join(test_path, "nnUNet_results"),
+        }
+
+    def test_missing_nnunetv2_raises_optional_import_error(self) -> None:
+        """A missing ``nnunetv2`` must be reported as such, not as a bare ``ModuleNotFoundError``."""
+        with mock.patch("monai.utils.module.optional_import", return_value=(None, False)):
+            with self.assertRaises(OptionalImportError) as context:
+                nnUNetV2Runner(input_config=dict(self.input_config))
+        self.assertIn("nnunetv2", str(context.exception))
+
+    def test_missing_nnunetv2_does_not_warn_about_the_dataset(self) -> None:
+        """The dataset lookup warning must not fire when the real cause is the missing package."""
+        with mock.patch("monai.utils.module.optional_import", return_value=(None, False)):
+            with self.assertNoLogs("monai.apps.nnunet.nnunetv2_runner", level="WARNING"):
+                with self.assertRaises(OptionalImportError):
+                    nnUNetV2Runner(input_config=dict(self.input_config))
+
+    def tearDown(self) -> None:
+        self.test_dir.cleanup()
+
+
+if __name__ == "__main__":
+    unittest.main()