fix(settings): keep the language and save settings one after the other

src/pages/SettingsPage.test.jsx

@@ -1,6 +1,6 @@
 // @vitest-environment jsdom
 import {afterEach, beforeEach, describe, expect, it, vi} from 'vitest';
-import {cleanup, fireEvent, render, screen, waitFor, within} from '@testing-library/react';
+import {act, cleanup, fireEvent, render, screen, waitFor, within} from '@testing-library/react';
 import {MemoryRouter} from 'react-router-dom';
 import SettingsPage from './SettingsPage.jsx';
 import {PreferencesProvider} from '../context/PreferencesContext.jsx';
@@ -29,6 +29,24 @@ function renderPage(me) {
     render(<MemoryRouter><PreferencesProvider><SettingsPage/></PreferencesProvider></MemoryRouter>);
 }
 
+/**
+ * Auth with PUT /api/users/settings answered one by one through answer(); GET /api/users/me shows what was saved.
+ */
+function fakeAuth(me) {
+    const saved = structuredClone(me);
+    const open = [];
+    globalThis.fetch = vi.fn((url, init) => {
+        if (init?.method !== 'PUT') return Promise.resolve({ok: true, status: 200, json: async () => structuredClone(saved)});
+        return new Promise((resolve) => open.push(() => {
+            const body = JSON.parse(init.body);
+            saved.displayName = body.displayName;
+            Object.assign(saved.settings, {useDarkTheme: body.useDarkTheme, language: body.language, publicProfile: body.publicProfile});
+            resolve({ok: true, status: 204, json: async () => { throw new SyntaxError('no body'); }});
+        }));
+    });
+    return {answer: () => open.shift()()};
+}
+
 describe('SettingsPage public profile', () => {
     beforeEach(() => localStorage.setItem('tbp_session', '1'));
 
@@ -46,6 +64,20 @@ describe('SettingsPage public profile', () => {
         expect(puts()[0].publicProfile).toBe(true);
     });
 
+    it('builds a save on the one before it, also while that one is still open', async () => {
+        const auth = fakeAuth(profile());
+        render(<MemoryRouter><PreferencesProvider><SettingsPage/></PreferencesProvider></MemoryRouter>);
+
+        fireEvent.click(await screen.findByRole('switch', {name: 'SETTINGS.PUBLIC_PROFILE'}));
+        await waitFor(() => expect(puts()).toHaveLength(1));
+        fireEvent.click(screen.getByRole('switch', {name: 'SETTINGS.DARK_THEME'}));
+        await act(async () => auth.answer());
+
+        await waitFor(() => expect(puts()).toHaveLength(2));
+        expect(puts()[1]).toMatchObject({publicProfile: false, useDarkTheme: false, displayName: 'Lobo'});
+        await act(async () => auth.answer());
+    });
+
     it('turns the public profile off and shows the link while it is on', async () => {
         renderPage(profile());