fix circular import error with loaded datalad-next

This commit fixes a circular import error that
occurs when datalad-next is loaded and tests are
patched. The error is described in
<datalad/datalad-next#716>

The reason for the import error is that importing
datalad_catalog.add from the module-level context
in datalad_catalog.tests.test_add, will import
datalad_next, which will in turn import certain
tests, which will trigger the extension-api
generation process, which tries to process
datalad_catalog.add, which is not yet
completely loaded.

datalad_catalog/add.py

@@ -23,9 +23,6 @@
     eval_results,
     get_status_dict,
 )
-from datalad_next.constraints import (
-    EnsurePath,
-)
 from datalad_next.exceptions import CapturedException
 
 import json
@@ -44,6 +41,8 @@ class AddParameterValidator(EnsureCommandParameterization):
     """"""
 
     def __init__(self):
+        from datalad_next.constraints import EnsurePath
+
         super().__init__(
             param_constraints=dict(
                 catalog=CatalogRequired() & EnsureWebCatalog(),

datalad_catalog/tests/test_add.py

@@ -2,7 +2,6 @@
     assert_in_results,
     assert_result_count,
 )
-from datalad_catalog.add import Add
 
 import io
 import json
@@ -11,11 +10,12 @@
 
 from datalad_next.constraints.exceptions import CommandParametrizationError
 
-catalog_add = Add()
-
 
 def test_no_args(demo_catalog, test_data):
+    from datalad_catalog.add import Add
+
     """Both the catalog and metadata arguments are required"""
+    catalog_add = Add()
     with pytest.raises(CommandParametrizationError):
         catalog_add()
 
@@ -28,6 +28,9 @@ def test_no_args(demo_catalog, test_data):
 
 def test_add_from_file(demo_catalog, test_data):
     """Add catalog metadata from a file with json line(s)"""
+    from datalad_catalog.add import Add
+
+    catalog_add = Add()
     res = catalog_add(
         catalog=demo_catalog,
         metadata=test_data.catalog_metadata_dataset1,
@@ -57,6 +60,9 @@ def test_add_from_file(demo_catalog, test_data):
 def test_add_from_file_faulty(demo_catalog, test_data):
     """Add catalog metadata from a file with json lines
     where at least one line is not valid json"""
+    from datalad_catalog.add import Add
+
+    catalog_add = Add()
     res = catalog_add(
         catalog=demo_catalog,
         metadata=test_data.catalog_metadata_valid_invalid,
@@ -80,10 +86,13 @@ def test_add_from_file_faulty(demo_catalog, test_data):
 
 def test_add_from_stdin(monkeypatch, demo_catalog):
     """Add catalog metadata from stdin"""
+    from datalad_catalog.add import Add
+
     mdata1 = '{"dataset_id": "deabeb9b-7a37-4062-a1e0-8fcef7909609", "dataset_version": "0321dbde969d2f5d6b533e35b5c5c51ac0b15758", "type": "dataset", "metadata_sources": {"key_source_map": {}, "sources": [{"source_name": "", "source_version": ""}]}}'
     mdata2 = '{"dataset_id": "3344ffv5-7a37-4062-a1e0-8fcef7909609", "dataset_version": "8888dbde969d2f5d6b533e35b5c5c51ac0b15758", "type": "dataset", "metadata_sources": {"key_source_map": {}, "sources": [{"source_name": "", "source_version": ""}]}}'
     content = io.StringIO(json.dumps(mdata1) + "\n" + json.dumps(mdata2))
     monkeypatch.setattr("sys.stdin", content)
+    catalog_add = Add()
     res = catalog_add(
         catalog=demo_catalog,
         metadata="-",
@@ -101,7 +110,10 @@ def test_add_from_stdin(monkeypatch, demo_catalog):
 
 def test_add_from_json_str(demo_catalog, test_data):
     """Add catalog metadata from a json serialized string"""
+    from datalad_catalog.add import Add
+
     mdata = '{"dataset_id": "deabeb9b-7a37-4062-a1e0-8fcef7909609", "dataset_version": "0321dbde969d2f5d6b533e35b5c5c51ac0b15758", "type": "dataset", "metadata_sources": {"key_source_map": {}, "sources": [{"source_name": "", "source_version": ""}]}}'
+    catalog_add = Add()
     res = catalog_add(
         catalog=demo_catalog,
         metadata=mdata,
@@ -118,6 +130,8 @@ def test_add_from_json_str(demo_catalog, test_data):
 
 def test_add_from_dict(demo_catalog):
     """Add catalog metadata from a json serialized string"""
+    from datalad_catalog.add import Add
+
     mdata = {
         "dataset_id": "deabeb9b-7a37-4062-a1e0-8fcef7909609",
         "dataset_version": "0321dbde969d2f5d6b533e35b5c5c51ac0b15758",
@@ -127,6 +141,7 @@ def test_add_from_dict(demo_catalog):
             "sources": [{"source_name": "", "source_version": ""}],
         },
     }
+    catalog_add = Add()
     res = catalog_add(
         catalog=demo_catalog,
         metadata=mdata,