test(useAddFavorite): add unit test for addFavorite mutation and erro…

…r handling

src/components/LibraryPage/components/Books/components/BookCard/components/FavoriteButton/hooks/useAddFavorite.test.tsx

@@ -0,0 +1,67 @@
+import { InMemoryCache, useMutation } from "@apollo/client";
+import { renderHook, act } from "@testing-library/react";
+import { MockedProvider } from "@apollo/client/testing";
+import { ReactNode } from "react";
+import { vi } from "vitest";
+
+import { useAddFavorite } from "./useAddFavorite";
+
+vi.mock("@apollo/client");
+describe("useAddFavorite", () => {
+  const bookId = "abc123";
+  const cache = new InMemoryCache();
+  const addFavoriteMock = vi.fn();
+
+  const wrapper = ({ children }: { children: ReactNode }) => (
+    <MockedProvider cache={cache}>{children}</MockedProvider>
+  );
+
+  it("adds favorite when called", async () => {
+    (useMutation as jest.Mock).mockImplementation(() => {
+      return [
+        addFavoriteMock,
+        { loading: false, error: undefined, data: undefined },
+      ];
+    });
+    const { result } = renderHook(() => useAddFavorite(), { wrapper });
+
+    act(() => {
+      result.current.addFavorite({ variables: { bookId } });
+    });
+
+    // Check that the mutation was called with the correct variables
+    expect(addFavoriteMock).toHaveBeenCalledWith({
+      variables: { bookId },
+    });
+    // Check that the mutation did not result in an error
+    expect(result.current.addError).toBeUndefined();
+  });
+
+  it("handles loading state", () => {
+    const mutationResult = { loading: true, error: undefined, data: undefined };
+    (useMutation as jest.Mock).mockReturnValue([
+      addFavoriteMock,
+      mutationResult,
+    ]);
+
+    const { result } = renderHook(() => useAddFavorite(), { wrapper });
+
+    expect(result.current.addLoading).toBe(true);
+  });
+
+  it("handles error state", () => {
+    const mutationResult = {
+      loading: false,
+      error: new Error("Mutation error"),
+      data: undefined,
+    };
+    (useMutation as jest.Mock).mockReturnValue([
+      addFavoriteMock,
+      mutationResult,
+    ]);
+
+    const { result } = renderHook(() => useAddFavorite(), { wrapper });
+
+    expect(result.current.addError).toEqual(new Error("Mutation error"));
+  });
+});