fix issue with commenting on exemplar docs

cypress/e2e/functional/teacher_tests/teacher_sort_work_view_spec.js

@@ -209,6 +209,7 @@ describe('SortWorkView Tests', () => {
     cy.visit(queryParams2);
     cy.waitForLoad();
     cy.openTopTab('sort-work');
+    cy.get('.section-header-label').should("contain", "Group 5");
     cy.get('.section-header-arrow').click({multiple: true}); // Open the sections
     cy.wait(1000);
     studentProblemDocs.forEach(doc => {
@@ -307,11 +308,6 @@ describe('SortWorkView Tests', () => {
     cy.log("check that exemplar document is displayed in new tag");
     chatPanel.getChatCloseButton().click();
     cy.openTopTab('sort-work');
-    // at the moment this is required to refresh the sort
-    sortWork.getShowForMenu().click();
-    sortWork.getShowForInvestigationOption().click();
-    sortWork.getShowForMenu().click();
-    sortWork.getShowForProblemOption().click();
 
     cy.get('.section-header-arrow').click({multiple: true}); // Open the sections
     sortWork.checkDocumentInGroup("Diverging Designs", exemplarDocs[0]);

src/models/stores/sorted-documents.ts

@@ -201,10 +201,18 @@ export class SortedDocuments {
       typecheck(DocumentMetadataModel, data);
       const exemplarMetadata = this.exemplarMetadataDocs.get(data.key);
       if (exemplarMetadata) {
+        // If this metadata doc in Firestore is an exemplar in the same unit then the exemplar
+        // metadata will be found. This will happen when a teacher comments on a exemplar.
+        // So in this case we need to merge the strategies from the exemplar with the strategies from
+        // the teacher's comments.
         const authoredStrategies = exemplarMetadata.strategies || [];
         const userStrategies = data.strategies || [];
         data.strategies = union(authoredStrategies, userStrategies);
-        data.tools = exemplarMetadata.tools;
+        // We also update the tools incase the author has changed the exemplar content after
+        // the teacher commented on the document.
+        // We need a copy of the tools so the same array isn't attached to two MST trees at
+        // the same time.
+        data.tools = [...exemplarMetadata.tools];
       }
     });
     return mstSnapshot;