test: align storage mocks with web storage semantics

Author: gildesmarais

frontend/src/__tests__/App.contract.test.tsx

@@ -161,6 +161,6 @@ describe('App contract', () => {
 
     expect(screen.getByText('Add access token')).toBeInTheDocument();
     expect(screen.queryByText('Feed generation failed')).not.toBeInTheDocument();
-    expect(globalThis.localStorage.getItem('html2rss_access_token')).toBeUndefined();
+    expect(globalThis.localStorage.getItem('html2rss_access_token')).toBeNull();
   });
 });

frontend/src/__tests__/setup.ts

@@ -29,7 +29,8 @@ const createStorageMock = () => {
       get length() {
         return store.size;
       },
-      getItem: vi.fn((key: string) => (store.has(key) ? store.get(key)! : undefined)),
+      // eslint-disable-next-line unicorn/no-null -- Web Storage returns null for missing keys.
+      getItem: vi.fn((key: string) => (store.has(key) ? store.get(key)! : null)),
       setItem: vi.fn((key: string, value: string) => {
         store.set(key, value);
       }),
@@ -39,7 +40,8 @@ const createStorageMock = () => {
       clear: vi.fn(() => {
         store.clear();
       }),
-      key: vi.fn((index: number) => [...store.keys()][index] ?? undefined),
+      // eslint-disable-next-line unicorn/no-null -- Web Storage key() returns null for out-of-range indexes.
+      key: vi.fn((index: number) => [...store.keys()][index] ?? null),
     },
   };
 };
@@ -49,10 +51,14 @@ const session = createStorageMock();
 
 Object.defineProperty(globalThis, 'localStorage', {
   value: local.api,
+  configurable: true,
+  writable: true,
 });
 
 Object.defineProperty(globalThis, 'sessionStorage', {
   value: session.api,
+  configurable: true,
+  writable: true,
 });
 
 beforeEach(() => {

frontend/src/__tests__/useAccessToken.test.ts

@@ -27,7 +27,7 @@ describe('useAccessToken', () => {
     expect(result.current.isLoading).toBe(false);
     expect(result.current.token).toBe('legacy-token');
     expect(globalThis.localStorage.getItem('html2rss_access_token')).toBe('legacy-token');
-    expect(globalThis.sessionStorage.getItem('html2rss_access_token')).toBeUndefined();
+    expect(globalThis.sessionStorage.getItem('html2rss_access_token')).toBeNull();
   });
 
   it('saves new tokens to the persistent storage path', async () => {
@@ -40,7 +40,7 @@ describe('useAccessToken', () => {
     expect(result.current.token).toBe('new-token');
     expect(result.current.hasToken).toBe(true);
     expect(globalThis.localStorage.getItem('html2rss_access_token')).toBe('new-token');
-    expect(globalThis.sessionStorage.getItem('html2rss_access_token')).toBeUndefined();
+    expect(globalThis.sessionStorage.getItem('html2rss_access_token')).toBeNull();
   });
 
   it('clears both persistent and legacy token copies', async () => {
@@ -55,7 +55,7 @@ describe('useAccessToken', () => {
 
     expect(result.current.token).toBeUndefined();
     expect(result.current.hasToken).toBe(false);
-    expect(globalThis.localStorage.getItem('html2rss_access_token')).toBeUndefined();
-    expect(globalThis.sessionStorage.getItem('html2rss_access_token')).toBeUndefined();
+    expect(globalThis.localStorage.getItem('html2rss_access_token')).toBeNull();
+    expect(globalThis.sessionStorage.getItem('html2rss_access_token')).toBeNull();
   });
 });