fix: show/hide add unit button based on childAddable flag of parent in unit page (#2351)

Course unit page shows Add Unit option without checking whether the parent subsection allows adding children. This fixes it.

src/course-unit/CourseUnit.test.jsx

@@ -792,6 +792,28 @@ describe('<CourseUnit />', () => {
       .toHaveBeenCalledWith(`/course/${courseId}/container/${blockId}/${updatedAncestorsChild.id}`, { replace: true });
   });
 
+  it('Show or hide new unit button based on parent sequence childAddable action', async () => {
+    render(<RootWrapper />);
+    // The new unit button should be visible when childAddable is true
+    await screen.findByRole('button', { name: courseSequenceMessages.newUnitBtnText.defaultMessage });
+
+    const updatedCourseSectionVerticalData = cloneDeep(courseSectionVerticalMock);
+    // Set childAddable to false for sequence i.e. current units parent.
+    set(updatedCourseSectionVerticalData, 'xblock_info.ancestor_info.ancestors[0].actions.childAddable', false);
+    axiosMock
+      .onGet(getCourseSectionVerticalApiUrl(blockId))
+      .reply(200, {
+        ...updatedCourseSectionVerticalData,
+      });
+    render(<RootWrapper />);
+    // to wait for loading
+    screen.findByTestId('unit-header-title');
+    // The new unit button should not be visible when childAddable is false
+    expect(
+      screen.queryByRole('button', { name: courseSequenceMessages.newUnitBtnText.defaultMessage }),
+    ).not.toBeInTheDocument();
+  });
+
   it('the sequence unit is updated after changing the unit header', async () => {
     const user = userEvent.setup();
     render(<RootWrapper />);

src/course-unit/course-sequence/sequence-navigation/SequenceNavigationTabs.jsx

@@ -6,7 +6,7 @@ import { Plus as PlusIcon, ContentPasteGo as ContentPasteGoIcon } from '@openedx
 import { useIntl } from '@edx/frontend-platform/i18n';
 
 import { changeEditTitleFormOpen, updateQueryPendingStatus } from '../../data/slice';
-import { getCourseId, getSequenceId } from '../../data/selectors';
+import { getCourseUnitData, getCourseId, getSequenceId } from '../../data/selectors';
 import messages from '../messages';
 import { useIndexOfLastVisibleChild } from '../hooks';
 import SequenceNavigationDropdown from './SequenceNavigationDropdown';
@@ -20,6 +20,8 @@ const SequenceNavigationTabs = ({
   const navigate = useNavigate();
   const sequenceId = useSelector(getSequenceId);
   const courseId = useSelector(getCourseId);
+  const courseUnit = useSelector(getCourseUnitData);
+  const sequenceChildAddable = courseUnit?.ancestorInfo?.ancestors?.[0]?.actions?.childAddable;
 
   const [
     indexOfLastVisibleChild,
@@ -58,6 +60,7 @@ const SequenceNavigationTabs = ({
               isActive={unitId === buttonUnitId}
             />
           ))}
+          {sequenceChildAddable && (
           <Button
             className="sequence-navigation-tabs-action-btn"
             variant="outline-primary"
@@ -66,6 +69,7 @@ const SequenceNavigationTabs = ({
           >
             {intl.formatMessage(messages.newUnitBtnText)}
           </Button>
+          )}
           {showPasteUnit && (
             <Button
               className="sequence-navigation-tabs-action-btn"