refactor: Update test imports to use new modular structure

Refactored all test files in tests/changelog/ to import directly from the new modular structure instead of relying on backward compatibility imports from changelog_helper.py.

**Import mapping:**
- DiffStix: changelog_helper → core.diff_stix
- AttackChangesEncoder: changelog_helper → core.attack_changes_encoder
- AttackObjectVersion, version utils: changelog_helper → utils.version_utils
- STIX utilities: changelog_helper → utils.stix_utils
- URL utilities: changelog_helper → utils.url_utils
- HTML/markdown formatters: changelog_helper → formatters.html_output
- Layer output: changelog_helper → formatters.layer_output
- CLI argument parser: changelog_helper → cli.argument_parser

**Files updated (17 total):**
Core tests:
- test_versioning.py - version_utils imports
- test_stix_processing.py - stix_utils + url_utils imports
- test_change_detection.py - stix_utils + version_utils imports
- test_diffstix_methods.py - core.diff_stix import
- test_missing_functions.py - multiple module imports

Integration tests:
- test_diffstix_behavioral.py - core.diff_stix import
- test_diffstix_minimal_data.py - core.diff_stix import
- test_diffstix_multi_domain.py - core.diff_stix import
- test_regression_baseline.py - core.attack_changes_encoder import
- test_network.py - core.diff_stix import

Formatting tests:
- test_html_output.py - formatters.html_output imports
- test_json_output.py - core.attack_changes_encoder + utils.version_utils imports
- test_layer_output.py - formatters.layer_output import
- test_markdown_output.py - formatters.html_output + utils.version_utils imports

Other:
- conftest.py - core.diff_stix import
- error_handling/test_errors.py - core.diff_stix + utils.version_utils imports
- cli/test_argument_handling.py - cli.argument_parser import

**Benefits:**
- Tests now use the actual module structure
- Clearer separation of concerns in test imports
- Removes dependency on backward compatibility layer
- Makes module responsibilities more explicit
- Easier to identify which module a function belongs to

Author: claude

tests/changelog/cli/test_argument_handling.py

@@ -4,7 +4,7 @@
 
 import pytest
 
-from mitreattack.diffStix.changelog_helper import get_parsed_args
+from mitreattack.diffStix.cli.argument_parser import get_parsed_args
 
 
 class TestArgumentHandling:

tests/changelog/conftest.py

@@ -12,7 +12,7 @@
 
 import pytest
 
-from mitreattack.diffStix.changelog_helper import DiffStix
+from mitreattack.diffStix.core.diff_stix import DiffStix
 
 # Import test utilities
 from tests.changelog.test_utils import (

tests/changelog/core/test_change_detection.py

@@ -1,9 +1,7 @@
 """Tests for change detection and grouping logic."""
 
-from mitreattack.diffStix.changelog_helper import (
-    cleanup_values,
-    is_patch_change,
-)
+from mitreattack.diffStix.utils.stix_utils import cleanup_values
+from mitreattack.diffStix.utils.version_utils import is_patch_change
 
 
 class TestChangeDetection:

tests/changelog/core/test_diffstix_methods.py

@@ -2,7 +2,7 @@
 
 import pytest
 
-from mitreattack.diffStix.changelog_helper import DiffStix
+from mitreattack.diffStix.core.diff_stix import DiffStix
 
 
 class TestDiffStixMethods:

tests/changelog/core/test_missing_functions.py

@@ -3,14 +3,11 @@
 import json
 from pathlib import Path
 
-from mitreattack.diffStix.changelog_helper import (
-    AttackChangesEncoder,
-    AttackObjectVersion,
-    get_relative_data_component_url,
-    layers_dict_to_files,
-    markdown_to_html,
-    write_detailed_html,
-)
+from mitreattack.diffStix.core.attack_changes_encoder import AttackChangesEncoder
+from mitreattack.diffStix.formatters.html_output import markdown_to_html, write_detailed_html
+from mitreattack.diffStix.formatters.layer_output import layers_dict_to_files
+from mitreattack.diffStix.utils.url_utils import get_relative_data_component_url
+from mitreattack.diffStix.utils.version_utils import AttackObjectVersion
 
 
 class TestMissingFunctions:

tests/changelog/core/test_stix_processing.py

@@ -1,11 +1,7 @@
 """Tests for STIX object processing functionality."""
 
-from mitreattack.diffStix.changelog_helper import (
-    deep_copy_stix,
-    get_attack_id,
-    get_relative_url_from_stix,
-    has_subtechniques,
-)
+from mitreattack.diffStix.utils.stix_utils import deep_copy_stix, get_attack_id, has_subtechniques
+from mitreattack.diffStix.utils.url_utils import get_relative_url_from_stix
 
 
 class TestStixProcessing:

tests/changelog/core/test_versioning.py

@@ -2,7 +2,7 @@
 
 import pytest
 
-from mitreattack.diffStix.changelog_helper import (
+from mitreattack.diffStix.utils.version_utils import (
     AttackObjectVersion,
     get_attack_object_version,
     is_major_version_change,

tests/changelog/error_handling/test_errors.py

@@ -4,10 +4,8 @@
 
 import pytest
 
-from mitreattack.diffStix.changelog_helper import (
-    DiffStix,
-    get_attack_object_version,
-)
+from mitreattack.diffStix.core.diff_stix import DiffStix
+from mitreattack.diffStix.utils.version_utils import get_attack_object_version
 
 
 class TestErrorHandling:

tests/changelog/formatting/test_html_output.py

@@ -2,7 +2,7 @@
 
 import json
 
-from mitreattack.diffStix.changelog_helper import markdown_to_html, write_detailed_html
+from mitreattack.diffStix.formatters.html_output import markdown_to_html, write_detailed_html
 
 
 class TestHtmlOutput:

tests/changelog/formatting/test_json_output.py

@@ -2,7 +2,8 @@
 
 import json
 
-from mitreattack.diffStix.changelog_helper import AttackChangesEncoder, AttackObjectVersion
+from mitreattack.diffStix.core.attack_changes_encoder import AttackChangesEncoder
+from mitreattack.diffStix.utils.version_utils import AttackObjectVersion
 
 
 class TestJsonOutput: