[MM-51302] Fix scroll to the bottom of editor after pasting long text (#22491)

Automatic Merge

e2e-tests/cypress/tests/integration/channels/collapsed_reply_threads/replies_spec.js

@@ -10,6 +10,8 @@
 // Stage: @prod
 // Group: @channels @collapsed_reply_threads
 
+import * as TIMEOUTS from '../../../fixtures/timeouts';
+
 describe('Collapsed Reply Threads', () => {
     let testTeam;
     let testUser;
@@ -174,4 +176,45 @@ describe('Collapsed Reply Threads', () => {
             cy.uiCloseRHS();
         });
     });
+
+    it('MM-T5413 should auto-scroll to bottom upon pasting long text in reply', () => {
+        // # Post a root post as current user
+        cy.postMessageAs({
+            sender: testUser,
+            message: 'Another interesting post,',
+            channelId: testChannel.id,
+        }).then(({id: rootId}) => {
+            // # Post multiple replies as other user so that the new messages line is pushed up
+            Cypress._.times(20, (i) => {
+                cy.postMessageAs({
+                    sender: otherUser,
+                    message: 'Reply ' + i,
+                    channelId: testChannel.id,
+                    rootId,
+                });
+            });
+
+            // # Click root post
+            cy.get(`#post_${rootId}`).click();
+
+            // # Wait for RHS to open and scroll to position
+            cy.wait(TIMEOUTS.ONE_SEC);
+
+            // * RHS should open and the editor's actions should not be visible.
+            cy.get('#rhsContainer').findByTestId('SendMessageButton').should('not.be.visible');
+
+            // # Close RHS
+            cy.uiCloseRHS();
+
+            // # Click root post
+            cy.get(`#post_${rootId}`).click();
+
+            // # Paste a multiline string in the RHS textbox.
+            const text = 'word '.repeat(2000);
+            cy.get('#rhsContainer').findByTestId('reply_textbox').clear().invoke('val', text).trigger('input');
+
+            // * RHS should open and the editor should be visible and focused
+            cy.get('#rhsContainer').findByTestId('SendMessageButton').should('be.visible');
+        });
+    });
 });