♻️ refactor(App): use react router

this adds `MainPage`

src/components/pages/MainPage/MainPage.test.tsx

@@ -0,0 +1,60 @@
+import { describe, it, expect, afterEach } from 'vitest'
+import { render, screen, cleanup } from '@testing-library/react'
+import userEvent from '@testing-library/user-event'
+
+import MainPage from './MainPage'
+
+// Tests
+describe('Renders main page correctly', async () => {
+  /**
+   * Resets all renders after each test
+   */
+  afterEach(() => {
+    cleanup()
+  })
+
+  /**
+   * Passes - shows title correctly
+   */
+  it('Should render the page correctly', async () => {
+    // Setup
+    await render(<MainPage />)
+    const h1 = await screen.queryByText('Vite + React')
+
+    // Post Expectations
+    expect(h1).toBeInTheDocument()
+  })
+
+  /**
+   * Passes - shows the button count correctly present
+   */
+  it('Should show the button count set to 0', async () => {
+    // Setup
+    await render(<MainPage />)
+    const button = await screen.queryByText('count is 0')
+
+    // Expectations
+    expect(button).toBeInTheDocument()
+  })
+
+  /**
+   * Passes - clicks the button 3 times and shows the correct count
+   */
+  it('Should show the button count set to 3', async () => {
+    // Setup
+    const user = userEvent.setup()
+    await render(<MainPage />)
+    const button = await screen.queryByText('count is 0')
+
+    // Pre Expectations
+    expect(button).toBeInTheDocument()
+
+    // Actions
+    await user.click(button as HTMLElement)
+    await user.click(button as HTMLElement)
+    await user.click(button as HTMLElement)
+
+    // Post Expectations
+    expect(button?.innerHTML).toBe('count is 3')
+  })
+})