diff --git a/src/app/__tests__/main-content.test.tsx b/src/app/__tests__/main-content.test.tsx
new file mode 100644
index 0000000..eb36de6
--- /dev/null
+++ b/src/app/__tests__/main-content.test.tsx
@@ -0,0 +1,133 @@
+import { test, expect, vi, afterEach } from "vitest";
+import { render, screen, cleanup } from "@testing-library/react";
+import userEvent from "@testing-library/user-event";
+import { MainContent } from "../main-content";
+
+vi.mock("@/lib/contexts/file-system-context", () => ({
+  FileSystemProvider: ({ children }: any) => <>{children}</>,
+  useFileSystem: () => ({
+    getAllFiles: () => new Map(),
+    refreshTrigger: 0,
+    selectedFile: null,
+    setSelectedFile: vi.fn(),
+  }),
+}));
+
+vi.mock("@/lib/contexts/chat-context", () => ({
+  ChatProvider: ({ children }: any) => <>{children}</>,
+  useChat: () => ({
+    messages: [],
+    input: "",
+    handleInputChange: vi.fn(),
+    handleSubmit: vi.fn(),
+    status: "idle",
+  }),
+}));
+
+vi.mock("@/components/chat/ChatInterface", () => ({
+  ChatInterface: () => <div data-testid="chat-interface" />,
+}));
+
+vi.mock("@/components/preview/PreviewFrame", () => ({
+  PreviewFrame: () => <div data-testid="preview-frame" />,
+}));
+
+vi.mock("@/components/editor/CodeEditor", () => ({
+  CodeEditor: () => <div data-testid="code-editor" />,
+}));
+
+vi.mock("@/components/editor/FileTree", () => ({
+  FileTree: () => <div data-testid="file-tree" />,
+}));
+
+vi.mock("@/components/HeaderActions", () => ({
+  HeaderActions: () => <div data-testid="header-actions" />,
+}));
+
+vi.mock("@/components/ui/resizable", () => ({
+  ResizablePanelGroup: ({ children }: any) => <div>{children}</div>,
+  ResizablePanel: ({ children }: any) => <div>{children}</div>,
+  ResizableHandle: () => <div />,
+}));
+
+afterEach(() => {
+  cleanup();
+  vi.clearAllMocks();
+});
+
+test("shows preview view by default", () => {
+  render(<MainContent />);
+
+  expect(screen.getByTestId("preview-frame")).toBeDefined();
+  expect(screen.queryByTestId("code-editor")).toBeNull();
+  expect(screen.queryByTestId("file-tree")).toBeNull();
+});
+
+test("Preview tab is active by default", () => {
+  render(<MainContent />);
+
+  const previewTab = screen.getByRole("tab", { name: "Preview" });
+  const codeTab = screen.getByRole("tab", { name: "Code" });
+
+  expect(previewTab.getAttribute("data-state")).toBe("active");
+  expect(codeTab.getAttribute("data-state")).toBe("inactive");
+});
+
+test("switches to code view when Code tab is clicked", async () => {
+  const user = userEvent.setup();
+  render(<MainContent />);
+
+  expect(screen.getByTestId("preview-frame")).toBeDefined();
+
+  await user.click(screen.getByRole("tab", { name: "Code" }));
+
+  expect(screen.queryByTestId("preview-frame")).toBeNull();
+  expect(screen.getByTestId("code-editor")).toBeDefined();
+  expect(screen.getByTestId("file-tree")).toBeDefined();
+});
+
+test("Code tab becomes active after clicking it", async () => {
+  const user = userEvent.setup();
+  render(<MainContent />);
+
+  await user.click(screen.getByRole("tab", { name: "Code" }));
+
+  const previewTab = screen.getByRole("tab", { name: "Preview" });
+  const codeTab = screen.getByRole("tab", { name: "Code" });
+
+  expect(codeTab.getAttribute("data-state")).toBe("active");
+  expect(previewTab.getAttribute("data-state")).toBe("inactive");
+});
+
+test("switches back to preview view when Preview tab is clicked", async () => {
+  const user = userEvent.setup();
+  render(<MainContent />);
+
+  await user.click(screen.getByRole("tab", { name: "Code" }));
+  expect(screen.getByTestId("code-editor")).toBeDefined();
+
+  await user.click(screen.getByRole("tab", { name: "Preview" }));
+
+  expect(screen.getByTestId("preview-frame")).toBeDefined();
+  expect(screen.queryByTestId("code-editor")).toBeNull();
+});
+
+test("can toggle between views multiple times", async () => {
+  const user = userEvent.setup();
+  render(<MainContent />);
+
+  // Start: preview
+  expect(screen.getByTestId("preview-frame")).toBeDefined();
+
+  // Switch to code
+  await user.click(screen.getByRole("tab", { name: "Code" }));
+  expect(screen.getByTestId("code-editor")).toBeDefined();
+
+  // Switch back to preview
+  await user.click(screen.getByRole("tab", { name: "Preview" }));
+  expect(screen.getByTestId("preview-frame")).toBeDefined();
+
+  // Switch to code again
+  await user.click(screen.getByRole("tab", { name: "Code" }));
+  expect(screen.getByTestId("code-editor")).toBeDefined();
+});
diff --git a/src/components/preview/PreviewFrame.tsx b/src/components/preview/PreviewFrame.tsx
index f6a8e5c..530a1e7 100644
--- a/src/components/preview/PreviewFrame.tsx
+++ b/src/components/preview/PreviewFrame.tsx
@@ -13,18 +13,13 @@ export function PreviewFrame() {
   const { getAllFiles, refreshTrigger } = useFileSystem();
   const [error, setError] = useState<string | null>(null);
   const [entryPoint, setEntryPoint] = useState<string>("/App.jsx");
-  const [isFirstLoad, setIsFirstLoad] = useState(true);
+  const isFirstLoadRef = useRef(true);
 
   useEffect(() => {
     const updatePreview = () => {
       try {
         const files = getAllFiles();
 
-        // Clear error first when we have files
-        if (files.size > 0 && error) {
-          setError(null);
-        }
-
         // Find the entry point - look for App.jsx, App.tsx, index.jsx, or index.tsx
         let foundEntryPoint = entryPoint;
         const possibleEntries = [
@@ -54,7 +49,7 @@ export function PreviewFrame() {
         }
 
         if (files.size === 0) {
-          if (isFirstLoad) {
+          if (isFirstLoadRef.current) {
             setError("firstLoad");
           } else {
             setError("No files to preview");
@@ -63,9 +58,7 @@ export function PreviewFrame() {
         }
 
         // We have files, so it's no longer the first load
-        if (isFirstLoad) {
-          setIsFirstLoad(false);
-        }
+        isFirstLoadRef.current = false;
 
         if (!foundEntryPoint || !files.has(foundEntryPoint)) {
           setError(
@@ -96,7 +89,7 @@ export function PreviewFrame() {
     };
 
     updatePreview();
-  }, [refreshTrigger, getAllFiles, entryPoint, error, isFirstLoad]);
+  }, [refreshTrigger, getAllFiles, entryPoint]);
 
   if (error) {
     if (error === "firstLoad") {