test(settings): Add regression test for group display names

Add Cypress E2E test to verify that group display names are shown
correctly in the user editor, even when the group ID differs from
the display name (e.g., when long group names get hashed).

The test creates a group with a very long name to trigger Nextcloud's
ID hashing behavior, assigns a user to that group, then verifies that
after a page reload the display name is shown instead of the hash ID.

Related to #55785

Signed-off-by: Claude <noreply@anthropic.com>

Co-Authored-By: Nikolaus Demmel <nikolaus@nikolaus-demmel.de>
Signed-off-by: Nikolaus Demmel <nikolaus@nikolaus-demmel.de>

Author: NikolausDemmel

cypress/e2e/settings/users_groups_display_name.cy.ts

@@ -0,0 +1,92 @@
+/**
+ * SPDX-FileCopyrightText: 2025 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ *
+ * Regression test for: https://github.com/nextcloud/server/issues/55785
+ *
+ * Tests that group display names are shown correctly in the user editor,
+ * even when the group ID differs from the display name (e.g., when long
+ * group names get hashed to create the group ID).
+ */
+
+import { User } from '@nextcloud/cypress'
+import { getUserListRow, handlePasswordConfirmation, toggleEditButton } from './usersUtils'
+
+// eslint-disable-next-line n/no-extraneous-import
+import randomString from 'crypto-random-string'
+
+const admin = new User('admin', 'admin')
+
+describe('Settings: Group names persist after reload (issue #55785)', () => {
+	let testUser: User
+	// Use a very long name to ensure Nextcloud hashes it to create the group ID.
+	// This creates a test case where group ID !== group display name.
+	const randomPart = randomString(80)
+	const groupName = `Test Group with Very Long Name ${randomPart}`
+
+	before(() => {
+		cy.createRandomUser().then((user) => {
+			testUser = user
+		})
+		cy.runOccCommand(`group:add '${groupName}'`).then(() => {
+			// Verify that the group ID is different from the display name
+			// (this confirms our test case is valid)
+			cy.runOccCommand('group:list --output=json').then((result) => {
+				const groups = JSON.parse(result.stdout)
+				const groupEntry = Object.entries(groups).find(([, displayName]) =>
+					(displayName as string).includes(randomPart)
+				)
+				if (groupEntry) {
+					const [groupId, displayName] = groupEntry
+					cy.log(`Group ID: ${groupId}`)
+					cy.log(`Display name: ${displayName}`)
+					// Assert that ID and name are different (this is what triggers the bug)
+					expect(groupId).to.not.equal(displayName)
+				}
+			})
+		})
+		cy.login(admin)
+		cy.intercept('GET', '**/ocs/v2.php/cloud/groups/details?search=&offset=*&limit=*').as('loadGroups')
+		cy.visit('/settings/users')
+		cy.wait('@loadGroups')
+	})
+
+	it('Assign user to group', () => {
+		toggleEditButton(testUser)
+
+		getUserListRow(testUser.userId)
+			.find('[data-cy-user-list-input-groups] input')
+			.click({ force: true })
+
+		getUserListRow(testUser.userId)
+			.find('[data-cy-user-list-input-groups] input')
+			.type(randomPart.slice(0, 10))
+
+		cy.contains('li.vs__dropdown-option', groupName)
+			.should('exist')
+			.click({ force: true })
+
+		handlePasswordConfirmation(admin.password)
+
+		toggleEditButton(testUser, false)
+	})
+
+	it('After page reload, selected group still shows correct name', () => {
+		// Visit the users page again to simulate a fresh page load
+		cy.visit('/settings/users')
+
+		toggleEditButton(testUser)
+
+		// Verify the selected group displays the name, not the hashed ID
+		getUserListRow(testUser.userId)
+			.find('[data-cy-user-list-input-groups]')
+			.should('exist')
+			.within(() => {
+				cy.get('.vs__selected').invoke('text').then((displayedText) => {
+					expect(displayedText.trim()).to.include('Test Group with Very Long Name')
+				})
+			})
+
+		toggleEditButton(testUser, false)
+	})
+})