test: cover new pair form flow

src/app/pairs/new/page.test.tsx

@@ -0,0 +1,108 @@
+import { act, fireEvent, render, screen, waitFor } from "@testing-library/react";
+import { useRouter } from "next/navigation";
+import { apiPost } from "../../../lib/apiClient";
+import NewPairPage from "./page";
+
+// Mock app navigation so the redirect can be asserted without changing routes.
+jest.mock("next/navigation", () => ({
+  useRouter: jest.fn(),
+}));
+
+// Mock the shared API client at the page boundary.
+jest.mock("../../../lib/apiClient", () => ({
+  apiPost: jest.fn(),
+}));
+
+const push = jest.fn();
+const mockUseRouter = useRouter as jest.Mock;
+const mockApiPost = apiPost as jest.MockedFunction<typeof apiPost>;
+
+function fillPairForm(source: string, destination: string) {
+  fireEvent.change(screen.getByLabelText("Source"), {
+    target: { value: source },
+  });
+  fireEvent.change(screen.getByLabelText("Destination"), {
+    target: { value: destination },
+  });
+}
+
+describe("NewPairPage", () => {
+  beforeEach(() => {
+    push.mockReset();
+    mockApiPost.mockReset();
+    mockUseRouter.mockReturnValue({ push });
+  });
+
+  it("renders the new pair form", () => {
+    render(<NewPairPage />);
+
+    expect(screen.getByRole("heading", { name: "New pair" })).toBeInTheDocument();
+    expect(screen.getByLabelText("Source")).toBeInTheDocument();
+    expect(screen.getByLabelText("Destination")).toBeInTheDocument();
+    expect(screen.getByRole("button", { name: "Register pair" })).toBeInTheDocument();
+  });
+
+  it("blocks identical source and destination without posting", async () => {
+    render(<NewPairPage />);
+
+    fillPairForm("USDC", "USDC");
+    fireEvent.click(screen.getByRole("button", { name: "Register pair" }));
+
+    expect(await screen.findByRole("alert")).toHaveTextContent(
+      "Source and destination must differ."
+    );
+    expect(mockApiPost).not.toHaveBeenCalled();
+    expect(push).not.toHaveBeenCalled();
+  });
+
+  it("posts the pair and redirects to the pairs page on success", async () => {
+    mockApiPost.mockResolvedValueOnce(undefined);
+    render(<NewPairPage />);
+
+    fillPairForm("USDC", "EURC");
+    fireEvent.click(screen.getByRole("button", { name: "Register pair" }));
+
+    await waitFor(() => {
+      expect(mockApiPost).toHaveBeenCalledWith("/api/v1/pairs", {
+        source: "USDC",
+        destination: "EURC",
+      });
+    });
+    expect(push).toHaveBeenCalledWith("/pairs");
+  });
+
+  it("surfaces server errors without redirecting", async () => {
+    mockApiPost.mockRejectedValueOnce(new Error("pair already exists"));
+    render(<NewPairPage />);
+
+    fillPairForm("USDC", "EURC");
+    fireEvent.click(screen.getByRole("button", { name: "Register pair" }));
+
+    expect(await screen.findByRole("alert")).toHaveTextContent("pair already exists");
+    expect(push).not.toHaveBeenCalled();
+  });
+
+  it("disables the submit button while saving", async () => {
+    let resolvePost!: () => void;
+    mockApiPost.mockReturnValueOnce(
+      new Promise<void>((resolve) => {
+        resolvePost = resolve;
+      })
+    );
+    render(<NewPairPage />);
+
+    fillPairForm("USDC", "EURC");
+    fireEvent.click(screen.getByRole("button", { name: "Register pair" }));
+
+    expect(screen.getByRole("button", { name: "Saving…" })).toBeDisabled();
+
+    await act(async () => {
+      resolvePost();
+    });
+
+    await waitFor(() => {
+      expect(push).toHaveBeenCalledWith("/pairs");
+    });
+    expect(screen.getByRole("button", { name: "Register pair" })).not.toBeDisabled();
+  });
+});