hdr: add BaseStoryPart._document_part

Author: scanny

docx/parts/story.py

@@ -28,4 +28,4 @@ def get_style_id(self, style_or_name, style_type):
     @lazyproperty
     def _document_part(self):
         """|DocumentPart| object for this package."""
-        raise NotImplementedError
+        return self.package.main_document_part

tests/parts/test_story.py

@@ -7,6 +7,7 @@
 import pytest
 
 from docx.enum.style import WD_STYLE_TYPE
+from docx.package import Package
 from docx.parts.document import DocumentPart
 from docx.parts.story import BaseStoryPart
 from docx.styles.style import BaseStyle
@@ -29,6 +30,14 @@ def it_can_get_a_style_id_by_style_or_name_and_type(
         document_part_.get_style_id.assert_called_once_with(style_, style_type)
         assert style_id == "BodyText"
 
+    def it_knows_the_main_document_part_to_help(self, package_, document_part_):
+        package_.main_document_part = document_part_
+        story_part = BaseStoryPart(None, None, None, package_)
+
+        document_part = story_part._document_part
+
+        assert document_part is document_part_
+
     # fixture components ---------------------------------------------
 
     @pytest.fixture
@@ -39,6 +48,10 @@ def document_part_(self, request):
     def _document_part_prop_(self, request):
         return property_mock(request, BaseStoryPart, "_document_part")
 
+    @pytest.fixture
+    def package_(self, request):
+        return instance_mock(request, Package)
+
     @pytest.fixture
     def style_(self, request):
         return instance_mock(request, BaseStyle)