Add support for loading files from Google Drive

#vibecoded

src/datasource/test_helpers.ts

@@ -0,0 +1,34 @@
+import {jest} from '@jest/globals';
+
+/**
+ * Mocks the global sessionStorage object and returns the underlying dictionary object
+ * that stores the items. This dictionary can be inspected or modified by tests.
+ */
+export function mockSessionStorage(): {[key: string]: string} {
+  const sessionStorageMock: {[key: string]: string} = {};
+  Object.defineProperty(global, 'sessionStorage', {
+    value: {
+      getItem: jest.fn((key: string) => sessionStorageMock[key] || null),
+      setItem: jest.fn((key: string, value: string) => {
+        sessionStorageMock[key] = value;
+      }),
+      removeItem: jest.fn((key: string) => {
+        delete sessionStorageMock[key];
+      }),
+      clear: jest.fn(() => {
+        for (const key in sessionStorageMock) {
+          delete sessionStorageMock[key];
+        }
+      }),
+      get length() {
+        return Object.keys(sessionStorageMock).length;
+      },
+      key: jest.fn((index: number) => {
+        return Object.keys(sessionStorageMock)[index] || null;
+      }),
+    },
+    writable: true,
+    configurable: true,
+  });
+  return sessionStorageMock;
+}