diff --git a/src/app/context/ThemeContext.test.tsx b/src/app/context/ThemeContext.test.tsx
new file mode 100644
index 0000000..50c9516
--- /dev/null
+++ b/src/app/context/ThemeContext.test.tsx
@@ -0,0 +1,34 @@
+import React, { useContext } from 'react'
+import { renderHook, act } from '@testing-library/react'
+import { ThemeContext, ThemeProvider } from './ThemeContext'
+
+const wrapper = ({ children }: { children: React.ReactNode }) => (
+  <ThemeProvider>{children as React.JSX.Element}</ThemeProvider>
+)
+
+describe('ThemeContext', () => {
+  beforeEach(() => {
+    localStorage.clear()
+  })
+
+  it('defaults to light when localStorage is empty', async () => {
+    const { result } = renderHook(() => useContext(ThemeContext), { wrapper })
+    await act(async () => {})
+    expect(result.current.theme).toBe('light')
+  })
+
+  it('hydrates to the stored theme on mount', async () => {
+    localStorage.setItem('theme', 'dark')
+    const { result } = renderHook(() => useContext(ThemeContext), { wrapper })
+    await act(async () => {})
+    expect(result.current.theme).toBe('dark')
+  })
+
+  it('changeTheme updates the theme and persists to localStorage', async () => {
+    const { result } = renderHook(() => useContext(ThemeContext), { wrapper })
+    await act(async () => {})
+    act(() => result.current.changeTheme('dark'))
+    expect(result.current.theme).toBe('dark')
+    expect(localStorage.getItem('theme')).toBe('dark')
+  })
+})
diff --git a/src/app/rss.xml/route.test.ts b/src/app/rss.xml/route.test.ts
new file mode 100644
index 0000000..f542cbe
--- /dev/null
+++ b/src/app/rss.xml/route.test.ts
@@ -0,0 +1,91 @@
+/**
+ * @jest-environment node
+ */
+import { getPosts } from '../util/posts'
+import { config } from '../config'
+import { formatDateToRFC822 } from './formatDateToRFC822'
+import { GET } from './route'
+import type { Post } from '../types'
+
+jest.mock('../util/posts', () => ({
+  getPosts: jest.fn(),
+}))
+
+const mockGetPosts = getPosts as jest.Mock
+
+function makePost(overrides: Partial<Post> = {}): Post {
+  return {
+    title: 'A Post',
+    slug: 'a-post',
+    description: 'A description',
+    date: new Date('2024-01-02T03:04:05Z'),
+    url: 'https://www.curtiscode.dev/post/a-post',
+    tags: ['foo'],
+    content: 'content',
+    ...overrides,
+  } as Post
+}
+
+async function getBody() {
+  const res = await GET()
+  return { res, body: await res.text() }
+}
+
+describe('rss.xml GET', () => {
+  afterEach(() => {
+    jest.clearAllMocks()
+  })
+
+  it('responds with application/xml content type', async () => {
+    mockGetPosts.mockReturnValue([makePost()])
+    const { res } = await getBody()
+    expect(res.headers.get('content-type')).toBe('application/xml')
+  })
+
+  it('uses the channel title, link and description from config', async () => {
+    mockGetPosts.mockReturnValue([makePost()])
+    const { body } = await getBody()
+    expect(body).toContain(`<title>${config.title}</title>`)
+    expect(body).toContain(`<link>${config.url}</link>`)
+    expect(body).toContain(`<description>${config.rssFeedDescription}</description>`)
+  })
+
+  it('renders one <item> per post', async () => {
+    mockGetPosts.mockReturnValue([
+      makePost({ url: 'https://www.curtiscode.dev/post/one' }),
+      makePost({ url: 'https://www.curtiscode.dev/post/two' }),
+      makePost({ url: 'https://www.curtiscode.dev/post/three' }),
+    ])
+    const { body } = await getBody()
+    expect((body.match(/<item>/g) ?? []).length).toBe(3)
+  })
+
+  it('renders a CDATA description only for posts that have one', async () => {
+    mockGetPosts.mockReturnValue([
+      makePost({ title: 'With Desc', description: 'Has a description' }),
+      makePost({ title: 'No Desc', description: undefined }),
+    ])
+    const { body } = await getBody()
+    expect(body).toContain('<![CDATA[ Has a description ]]>')
+    // One channel-level <description> plus exactly one item-level description
+    expect((body.match(/<description>/g) ?? []).length).toBe(2)
+  })
+
+  it('formats pubDate and lastBuildDate as RFC-822', async () => {
+    const date = new Date('2024-01-02T03:04:05Z')
+    mockGetPosts.mockReturnValue([makePost({ date })])
+    const { body } = await getBody()
+    const expected = formatDateToRFC822(date)
+    expect(body).toContain(`<pubDate>${expected}</pubDate>`)
+    expect(body).toContain(`<lastBuildDate>${expected}</lastBuildDate>`)
+  })
+
+  it('caps the feed at 50 items', async () => {
+    const posts = Array.from({ length: 60 }, (_, i) =>
+      makePost({ url: `https://www.curtiscode.dev/post/${i}` }),
+    )
+    mockGetPosts.mockReturnValue(posts)
+    const { body } = await getBody()
+    expect((body.match(/<item>/g) ?? []).length).toBe(50)
+  })
+})
diff --git a/src/app/sitemap.xml/route.test.ts b/src/app/sitemap.xml/route.test.ts
new file mode 100644
index 0000000..1cab02b
--- /dev/null
+++ b/src/app/sitemap.xml/route.test.ts
@@ -0,0 +1,106 @@
+/**
+ * @jest-environment node
+ */
+import { getPosts } from '../util/posts'
+import { config } from '../config'
+import { GET } from './route'
+import type { Post } from '../types'
+
+jest.mock('../util/posts', () => {
+  const actual = jest.requireActual('../util/posts')
+  return {
+    ...actual,
+    getPosts: jest.fn(),
+  }
+})
+
+const mockGetPosts = getPosts as jest.Mock
+
+function makePost(overrides: Partial<Post> = {}): Post {
+  return {
+    title: 'A Post',
+    slug: 'a-post',
+    date: new Date('2024-01-01T00:00:00.000Z'),
+    url: 'https://www.curtiscode.dev/post/a-post',
+    tags: ['foo'],
+    content: 'content',
+    ...overrides,
+  } as Post
+}
+
+function lastmodForTag(body: string, tag: string): string | null {
+  const re = new RegExp(
+    `<loc>${config.url}/tag/${tag}</loc>\\s*<lastmod>([^<]+)</lastmod>`,
+  )
+  const match = body.match(re)
+  return match ? match[1] : null
+}
+
+async function getBody() {
+  const res = await GET()
+  return { res, body: await res.text() }
+}
+
+describe('sitemap.xml GET', () => {
+  afterEach(() => {
+    jest.clearAllMocks()
+  })
+
+  const posts = [
+    makePost({
+      url: 'https://www.curtiscode.dev/post/a',
+      tags: ['foo'],
+      date: new Date('2024-01-01T00:00:00.000Z'),
+    }),
+    makePost({
+      url: 'https://www.curtiscode.dev/post/b',
+      tags: ['foo', 'bar'],
+      date: new Date('2024-03-01T00:00:00.000Z'),
+    }),
+    makePost({
+      url: 'https://www.curtiscode.dev/post/c',
+      tags: ['bar'],
+      date: new Date('2024-05-01T00:00:00.000Z'),
+    }),
+  ]
+
+  it('responds with application/xml content type', async () => {
+    mockGetPosts.mockReturnValue(posts)
+    const { res } = await getBody()
+    expect(res.headers.get('content-type')).toBe('application/xml')
+  })
+
+  it('includes the homepage url', async () => {
+    mockGetPosts.mockReturnValue(posts)
+    const { body } = await getBody()
+    expect(body).toContain('<loc>https://www.curtiscode.dev/</loc>')
+  })
+
+  it('includes a url for each post using the ISO date as lastmod', async () => {
+    mockGetPosts.mockReturnValue(posts)
+    const { body } = await getBody()
+    for (const post of posts) {
+      expect(body).toContain(`<loc>${post.url}</loc>`)
+      expect(body).toContain(`<lastmod>${post.date.toISOString()}</lastmod>`)
+    }
+  })
+
+  it('includes a url for each top tag', async () => {
+    mockGetPosts.mockReturnValue(posts)
+    const { body } = await getBody()
+    expect(body).toContain(`<loc>${config.url}/tag/foo</loc>`)
+    expect(body).toContain(`<loc>${config.url}/tag/bar</loc>`)
+  })
+
+  it('uses the newest post date as lastmod for each tag', async () => {
+    mockGetPosts.mockReturnValue(posts)
+    const { body } = await getBody()
+    // foo: newest is post b (2024-03-01); bar: newest is post c (2024-05-01)
+    expect(lastmodForTag(body, 'foo')).toBe(
+      new Date('2024-03-01T00:00:00.000Z').toISOString(),
+    )
+    expect(lastmodForTag(body, 'bar')).toBe(
+      new Date('2024-05-01T00:00:00.000Z').toISOString(),
+    )
+  })
+})