test: Split tests into conventionally named files

Replace test_new_features.py with three files following project conventions:
- test_diff_filtering.py — Diff.filter() and Diff.exclude()
- test_diffsync_diff_and_sync_parameters.py — model_types, filters,
  sync_attrs, exclude_attrs, sync_filter, concurrent, and combinations
- test_diffsync_model_bulk.py — bulk CRUD and store bulk operations

Converted from class-based to flat function style with Apache license
headers, matching the existing test structure.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: jdrew82

tests/unit/test_diff_filtering.py

@@ -0,0 +1,99 @@
+"""Unit tests for the Diff filter and exclude methods.
+
+Copyright (c) 2020-2021 Network To Code, LLC <info@networktocode.com>
+
+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.
+"""
+
+import pytest
+
+from diffsync.diff import Diff, DiffElement
+
+
+def test_diff_filter_by_action_create(diff_with_children):
+    """Filtering a Diff by action='create' should only retain elements with create diffs."""
+    filtered = diff_with_children.filter(actions={"create"})
+    actions = []
+    for child in filtered.get_children():
+        if child.action:
+            actions.append(child.action)
+    assert "create" in actions
+    assert "delete" not in actions
+
+
+def test_diff_filter_by_action_delete(diff_with_children):
+    """Filtering a Diff by action='delete' should only retain elements with delete diffs."""
+    filtered = diff_with_children.filter(actions={"delete"})
+    actions = []
+    for child in filtered.get_children():
+        if child.action:
+            actions.append(child.action)
+    assert "delete" in actions
+    assert "create" not in actions
+
+
+def test_diff_filter_by_model_types(diff_with_children):
+    """Filtering a Diff by model_types should only retain elements of those types."""
+    filtered = diff_with_children.filter(model_types={"person"})
+    types = [child.type for child in filtered.get_children()]
+    assert "person" in types
+    assert "device" not in types
+    assert "address" not in types
+
+
+def test_diff_filter_by_action_and_model_type(diff_with_children):
+    """Filtering by both action and model type should apply both criteria."""
+    filtered = diff_with_children.filter(actions={"create"}, model_types={"person"})
+    elements = list(filtered.get_children())
+    assert len(elements) == 1
+    assert elements[0].type == "person"
+    assert elements[0].action == "create"
+
+
+def test_diff_filter_does_not_mutate_original(diff_with_children):
+    """Calling filter() should return a new Diff without modifying the original."""
+    original_len = len(diff_with_children)
+    _ = diff_with_children.filter(actions={"create"})
+    assert len(diff_with_children) == original_len
+
+
+def test_diff_exclude_by_action(diff_with_children):
+    """Excluding by action should remove elements with that action."""
+    excluded = diff_with_children.exclude(actions={"delete"})
+    for child in excluded.get_children():
+        assert child.action != "delete"
+
+
+def test_diff_exclude_by_model_types(diff_with_children):
+    """Excluding by model_types should remove elements of those types."""
+    excluded = diff_with_children.exclude(model_types={"person"})
+    types = [child.type for child in excluded.get_children()]
+    assert "person" not in types
+
+
+def test_diff_filter_no_criteria_returns_full_copy(diff_with_children):
+    """Filtering with no criteria should return a copy of the entire Diff."""
+    filtered = diff_with_children.filter()
+    assert len(filtered) == len(diff_with_children)
+
+
+def test_diff_exclude_no_criteria_returns_full_copy(diff_with_children):
+    """Excluding with no criteria should return a copy of the entire Diff."""
+    excluded = diff_with_children.exclude()
+    assert len(excluded) == len(diff_with_children)
+
+
+def test_diff_filter_preserves_models_processed(diff_with_children):
+    """The models_processed count should be preserved on the filtered Diff."""
+    filtered = diff_with_children.filter(actions={"create"})
+    assert filtered.models_processed == diff_with_children.models_processed