test: cover ToastProvider behavior

src/components/__tests__/ToastProvider.test.tsx

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+import { act, fireEvent, render, screen } from "@testing-library/react";
+import { ToastProvider, useToast } from "../ToastProvider";
+
+function ToastHarness() {
+  const { push } = useToast();
+
+  return (
+    <div>
+      <button onClick={() => push("Saved route")}>Show info</button>
+      <button onClick={() => push("Route failed", "error")}>
+        Show error
+      </button>
+      <button
+        onClick={() => {
+          push("First route");
+          push("Second route");
+        }}
+      >
+        Show two
+      </button>
+    </div>
+  );
+}
+
+function MissingProviderHarness() {
+  useToast();
+  return null;
+}
+
+describe("ToastProvider", () => {
+  beforeEach(() => {
+    jest.useFakeTimers();
+  });
+
+  afterEach(() => {
+    act(() => {
+      jest.runOnlyPendingTimers();
+    });
+    jest.useRealTimers();
+  });
+
+  it("renders info toasts as polite status messages", () => {
+    render(
+      <ToastProvider>
+        <ToastHarness />
+      </ToastProvider>,
+    );
+
+    fireEvent.click(screen.getByRole("button", { name: "Show info" }));
+
+    expect(screen.getByRole("status")).toHaveTextContent("Saved route");
+    expect(screen.getByText("Saved route").parentElement).toHaveAttribute(
+      "aria-live",
+      "polite",
+    );
+  });
+
+  it("renders error toasts with an alert role", () => {
+    render(
+      <ToastProvider>
+        <ToastHarness />
+      </ToastProvider>,
+    );
+
+    fireEvent.click(screen.getByRole("button", { name: "Show error" }));
+
+    expect(screen.getByRole("alert")).toHaveTextContent("Route failed");
+  });
+
+  it("auto-dismisses toasts after four seconds", () => {
+    render(
+      <ToastProvider>
+        <ToastHarness />
+      </ToastProvider>,
+    );
+
+    fireEvent.click(screen.getByRole("button", { name: "Show info" }));
+    expect(screen.getByText("Saved route")).toBeInTheDocument();
+
+    act(() => {
+      jest.advanceTimersByTime(4000);
+    });
+
+    expect(screen.queryByText("Saved route")).not.toBeInTheDocument();
+  });
+
+  it("keeps multiple queued toasts visible until their timers expire", () => {
+    render(
+      <ToastProvider>
+        <ToastHarness />
+      </ToastProvider>,
+    );
+
+    fireEvent.click(screen.getByRole("button", { name: "Show two" }));
+
+    expect(screen.getByText("First route")).toBeInTheDocument();
+    expect(screen.getByText("Second route")).toBeInTheDocument();
+
+    act(() => {
+      jest.advanceTimersByTime(3999);
+    });
+
+    expect(screen.getByText("First route")).toBeInTheDocument();
+    expect(screen.getByText("Second route")).toBeInTheDocument();
+  });
+
+  it("throws a clear error when useToast is rendered outside the provider", () => {
+    const consoleError = jest.spyOn(console, "error").mockImplementation();
+
+    expect(() => render(<MissingProviderHarness />)).toThrow(
+      "useToast must be used inside <ToastProvider>",
+    );
+
+    consoleError.mockRestore();
+  });
+});