feat: add empty state to Changes tab with icon and message (#12237)

Co-authored-by: amanape <83104063+amanape@users.noreply.github.com>

frontend/__tests__/routes/changes-tab.test.tsx

@@ -0,0 +1,68 @@
+import { render, screen } from "@testing-library/react";
+import { QueryClient, QueryClientProvider } from "@tanstack/react-query";
+import { describe, expect, it, vi } from "vitest";
+import { MemoryRouter } from "react-router";
+import GitChanges from "#/routes/changes-tab";
+import { useUnifiedGetGitChanges } from "#/hooks/query/use-unified-get-git-changes";
+import { useAgentState } from "#/hooks/use-agent-state";
+import { AgentState } from "#/types/agent-state";
+
+vi.mock("react-i18next", () => ({
+  useTranslation: () => ({
+    t: (key: string) => key,
+  }),
+}));
+
+vi.mock("#/hooks/query/use-unified-get-git-changes");
+vi.mock("#/hooks/use-agent-state");
+vi.mock("#/hooks/use-conversation-id", () => ({
+  useConversationId: () => ({ conversationId: "test-id" }),
+}));
+
+const wrapper = ({ children }: { children: React.ReactNode }) => (
+  <MemoryRouter>
+    <QueryClientProvider client={new QueryClient()}>
+      {children}
+    </QueryClientProvider>
+  </MemoryRouter>
+);
+
+describe("Changes Tab", () => {
+  it("should show EmptyChangesMessage when there are no changes", () => {
+    vi.mocked(useUnifiedGetGitChanges).mockReturnValue({
+      data: [],
+      isLoading: false,
+      isSuccess: true,
+      isError: false,
+      error: null,
+      refetch: vi.fn(),
+    });
+    vi.mocked(useAgentState).mockReturnValue({
+      curAgentState: AgentState.RUNNING,
+    });
+
+    render(<GitChanges />, { wrapper });
+
+    expect(screen.getByText("DIFF_VIEWER$NO_CHANGES")).toBeInTheDocument();
+  });
+
+  it("should not show EmptyChangesMessage when there are changes", () => {
+    vi.mocked(useUnifiedGetGitChanges).mockReturnValue({
+      data: [{ path: "src/file.ts", status: "M" }],
+      isLoading: false,
+      isSuccess: true,
+      isError: false,
+      error: null,
+      refetch: vi.fn(),
+    });
+    vi.mocked(useAgentState).mockReturnValue({
+      curAgentState: AgentState.RUNNING,
+    });
+
+    render(<GitChanges />, { wrapper });
+
+    expect(
+      screen.queryByText("DIFF_VIEWER$NO_CHANGES"),
+    ).not.toBeInTheDocument();
+  });
+});