diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 8eeb714ca..e1523a10c 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -77,9 +77,9 @@ jobs:
       - uses: denoland/setup-deno@v1
         with:
           deno-version: v1.x
-      - run: env NAME=Deno deno test --coverage=coverage/raw/deno-runtime --allow-read --allow-env --allow-write --allow-net -c runtime-tests/deno/deno.json runtime-tests/deno
-      - run: deno test -c runtime-tests/deno-jsx/deno.precompile.json --coverage=coverage/raw/deno-precompile-jsx runtime-tests/deno-jsx
-      - run: deno test -c runtime-tests/deno-jsx/deno.react-jsx.json --coverage=coverage/raw/deno-react-jsx runtime-tests/deno-jsx
+      - run: env NAME=Deno deno test --coverage=coverage/raw/deno-runtime --allow-read --allow-env --allow-write --allow-net -c runtime_tests/deno/deno.json runtime_tests/deno
+      - run: deno test -c runtime_tests/deno-jsx/deno.precompile.json --coverage=coverage/raw/deno-precompile-jsx runtime_tests/deno-jsx
+      - run: deno test -c runtime_tests/deno-jsx/deno.react-jsx.json --coverage=coverage/raw/deno-react-jsx runtime_tests/deno-jsx
       - uses: actions/upload-artifact@v4
         with:
           name: coverage-deno
diff --git a/package.json b/package.json
index cc7bf9425..9ff375ac4 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "hono",
-  "version": "4.6.2",
+  "version": "4.6.1",
   "description": "Web framework built on Web Standards",
   "main": "dist/cjs/index.js",
   "type": "module",
@@ -12,18 +12,18 @@
   "scripts": {
     "test": "tsc --noEmit && vitest --run && vitest -c .vitest.config/jsx-runtime-default.ts --run && vitest -c .vitest.config/jsx-runtime-dom.ts --run",
     "test:watch": "vitest --watch",
-    "test:deno": "deno test --allow-read --allow-env --allow-write --allow-net -c runtime-tests/deno/deno.json runtime-tests/deno && deno test --no-lock -c runtime-tests/deno-jsx/deno.precompile.json runtime-tests/deno-jsx && deno test --no-lock -c runtime-tests/deno-jsx/deno.react-jsx.json runtime-tests/deno-jsx",
-    "test:bun": "bun test --jsx-import-source ../../src/jsx runtime-tests/bun/index.test.tsx",
-    "test:fastly": "vitest --run --config ./runtime-tests/fastly/vitest.config.ts",
-    "test:node": "vitest --run --config ./runtime-tests/node/vitest.config.ts",
-    "test:workerd": "vitest --run --config ./runtime-tests/workerd/vitest.config.ts",
-    "test:lambda": "vitest --run --config ./runtime-tests/lambda/vitest.config.ts",
-    "test:lambda-edge": "vitest --run --config ./runtime-tests/lambda-edge/vitest.config.ts",
+    "test:deno": "deno test --allow-read --allow-env --allow-write --allow-net -c runtime_tests/deno/deno.json runtime_tests/deno && deno test --no-lock -c runtime_tests/deno-jsx/deno.precompile.json runtime_tests/deno-jsx && deno test --no-lock -c runtime_tests/deno-jsx/deno.react-jsx.json runtime_tests/deno-jsx",
+    "test:bun": "bun test --jsx-import-source ../../src/jsx runtime_tests/bun/index.test.tsx",
+    "test:fastly": "vitest --run --config ./runtime_tests/fastly/vitest.config.ts",
+    "test:node": "vitest --run --config ./runtime_tests/node/vitest.config.ts",
+    "test:workerd": "vitest --run --config ./runtime_tests/workerd/vitest.config.ts",
+    "test:lambda": "vitest --run --config ./runtime_tests/lambda/vitest.config.ts",
+    "test:lambda-edge": "vitest --run --config ./runtime_tests/lambda-edge/vitest.config.ts",
     "test:all": "bun run test && bun test:deno && bun test:bun && bun test:fastly && bun test:node && bun test:workerd && bun test:lambda && bun test:lambda-edge",
-    "lint": "eslint src runtime-tests",
-    "lint:fix": "eslint src runtime-tests --fix",
-    "format": "prettier --check --cache \"src/**/*.{js,ts,tsx}\" \"runtime-tests/**/*.{js,ts,tsx}\"",
-    "format:fix": "prettier --write --cache --cache-strategy metadata \"src/**/*.{js,ts,tsx}\" \"runtime-tests/**/*.{js,ts,tsx}\"",
+    "lint": "eslint src runtime_tests",
+    "lint:fix": "eslint src runtime_tests --fix",
+    "format": "prettier --check --cache \"src/**/*.{js,ts,tsx}\" \"runtime_tests/**/*.{js,ts,tsx}\"",
+    "format:fix": "prettier --write --cache --cache-strategy metadata \"src/**/*.{js,ts,tsx}\" \"runtime_tests/**/*.{js,ts,tsx}\"",
     "copy:package.cjs.json": "cp ./package.cjs.json ./dist/cjs/package.json && cp ./package.cjs.json ./dist/types/package.json ",
     "build": "bun run --shell bun remove-dist && bun ./build.ts && bun run copy:package.cjs.json",
     "postbuild": "publint",
diff --git a/runtime-tests/deno/deno.lock b/runtime-tests/deno/deno.lock
deleted file mode 100644
index 49d0b042e..000000000
--- a/runtime-tests/deno/deno.lock
+++ /dev/null
@@ -1,34 +0,0 @@
-{
-  "version": "3",
-  "packages": {
-    "specifiers": {
-      "jsr:@std/assert@^1.0.3": "jsr:@std/assert@1.0.3",
-      "jsr:@std/internal@^1.0.2": "jsr:@std/internal@1.0.2",
-      "jsr:@std/testing@^1.0.1": "jsr:@std/testing@1.0.1"
-    },
-    "jsr": {
-      "@std/assert@1.0.3": {
-        "integrity": "b0d03ce1ced880df67132eea140623010d415848df66f6aa5df76507ca7c26d8",
-        "dependencies": [
-          "jsr:@std/internal@^1.0.2"
-        ]
-      },
-      "@std/internal@1.0.2": {
-        "integrity": "f4cabe2021352e8bfc24e6569700df87bf070914fc38d4b23eddd20108ac4495"
-      },
-      "@std/testing@1.0.1": {
-        "integrity": "9c25841137ee818933e1722091bb9ed5fdc251c35e84c97979a52196bdb6c5c3",
-        "dependencies": [
-          "jsr:@std/assert@^1.0.3"
-        ]
-      }
-    }
-  },
-  "remote": {},
-  "workspace": {
-    "dependencies": [
-      "jsr:@std/assert@^1.0.3",
-      "jsr:@std/testing@^1.0.1"
-    ]
-  }
-}
diff --git a/runtime-tests/bun/.static/plain.txt b/runtime_tests/bun/.static/plain.txt
similarity index 100%
rename from runtime-tests/bun/.static/plain.txt
rename to runtime_tests/bun/.static/plain.txt
diff --git a/runtime-tests/bun/favicon.ico b/runtime_tests/bun/favicon.ico
similarity index 100%
rename from runtime-tests/bun/favicon.ico
rename to runtime_tests/bun/favicon.ico
diff --git a/runtime-tests/bun/index.test.tsx b/runtime_tests/bun/index.test.tsx
similarity index 98%
rename from runtime-tests/bun/index.test.tsx
rename to runtime_tests/bun/index.test.tsx
index 8aaed909b..a9d4bddbc 100644
--- a/runtime-tests/bun/index.test.tsx
+++ b/runtime_tests/bun/index.test.tsx
@@ -83,10 +83,10 @@ describe('Basic Auth Middleware', () => {
 describe('Serve Static Middleware', () => {
   const app = new Hono()
   const onNotFound = vi.fn(() => {})
-  app.all('/favicon.ico', serveStatic({ path: './runtime-tests/bun/favicon.ico' }))
+  app.all('/favicon.ico', serveStatic({ path: './runtime_tests/bun/favicon.ico' }))
   app.all(
     '/favicon-notfound.ico',
-    serveStatic({ path: './runtime-tests/bun/favicon-notfound.ico', onNotFound })
+    serveStatic({ path: './runtime_tests/bun/favicon-notfound.ico', onNotFound })
   )
   app.use('/favicon-notfound.ico', async (c, next) => {
     await next()
@@ -95,14 +95,14 @@ describe('Serve Static Middleware', () => {
   app.get(
     '/static/*',
     serveStatic({
-      root: './runtime-tests/bun/',
+      root: './runtime_tests/bun/',
       onNotFound,
     })
   )
   app.get(
     '/dot-static/*',
     serveStatic({
-      root: './runtime-tests/bun/',
+      root: './runtime_tests/bun/',
       rewriteRequestPath: (path) => path.replace(/^\/dot-static/, './.static'),
     })
   )
@@ -121,7 +121,7 @@ describe('Serve Static Middleware', () => {
     expect(res.status).toBe(404)
     expect(res.headers.get('X-Custom')).toBe('Bun')
     expect(onNotFound).toHaveBeenCalledWith(
-      './runtime-tests/bun/favicon-notfound.ico',
+      './runtime_tests/bun/favicon-notfound.ico',
       expect.anything()
     )
   })
diff --git a/runtime-tests/bun/static/download b/runtime_tests/bun/static/download
similarity index 100%
rename from runtime-tests/bun/static/download
rename to runtime_tests/bun/static/download
diff --git a/runtime-tests/bun/static/hello.world/index.html b/runtime_tests/bun/static/hello.world/index.html
similarity index 100%
rename from runtime-tests/bun/static/hello.world/index.html
rename to runtime_tests/bun/static/hello.world/index.html
diff --git a/runtime-tests/bun/static/helloworld/index.html b/runtime_tests/bun/static/helloworld/index.html
similarity index 100%
rename from runtime-tests/bun/static/helloworld/index.html
rename to runtime_tests/bun/static/helloworld/index.html
diff --git a/runtime-tests/bun/static/plain.txt b/runtime_tests/bun/static/plain.txt
similarity index 100%
rename from runtime-tests/bun/static/plain.txt
rename to runtime_tests/bun/static/plain.txt
diff --git a/runtime-tests/bun/vitest.config.ts b/runtime_tests/bun/vitest.config.ts
similarity index 83%
rename from runtime-tests/bun/vitest.config.ts
rename to runtime_tests/bun/vitest.config.ts
index df1122b6c..6b1cae417 100644
--- a/runtime-tests/bun/vitest.config.ts
+++ b/runtime_tests/bun/vitest.config.ts
@@ -5,7 +5,7 @@ import config from '../../vitest.config'
 export default defineConfig({
   test: {
     globals: true,
-    include: ['**/runtime-tests/bun/**/*.+(ts|tsx|js)'],
+    include: ['**/runtime_tests/bun/**/*.+(ts|tsx|js)'],
     coverage: {
       ...config.test?.coverage,
       reportsDirectory: './coverage/raw/runtime-bun',
diff --git a/runtime-tests/deno-jsx/deno.precompile.json b/runtime_tests/deno-jsx/deno.precompile.json
similarity index 100%
rename from runtime-tests/deno-jsx/deno.precompile.json
rename to runtime_tests/deno-jsx/deno.precompile.json
diff --git a/runtime-tests/deno-jsx/deno.react-jsx.json b/runtime_tests/deno-jsx/deno.react-jsx.json
similarity index 100%
rename from runtime-tests/deno-jsx/deno.react-jsx.json
rename to runtime_tests/deno-jsx/deno.react-jsx.json
diff --git a/runtime-tests/deno-jsx/jsx.test.tsx b/runtime_tests/deno-jsx/jsx.test.tsx
similarity index 100%
rename from runtime-tests/deno-jsx/jsx.test.tsx
rename to runtime_tests/deno-jsx/jsx.test.tsx
diff --git a/runtime-tests/deno/.static/plain.txt b/runtime_tests/deno/.static/plain.txt
similarity index 100%
rename from runtime-tests/deno/.static/plain.txt
rename to runtime_tests/deno/.static/plain.txt
diff --git a/runtime-tests/deno/.vscode/settings.json b/runtime_tests/deno/.vscode/settings.json
similarity index 100%
rename from runtime-tests/deno/.vscode/settings.json
rename to runtime_tests/deno/.vscode/settings.json
diff --git a/runtime_tests/deno/cache.test.ts b/runtime_tests/deno/cache.test.ts
new file mode 100644
index 000000000..583a90cd8
--- /dev/null
+++ b/runtime_tests/deno/cache.test.ts
@@ -0,0 +1,132 @@
+import { expect } from '@std/expect'
+import { FakeTime } from '@std/testing/time'
+import { Hono } from '../../src/hono.ts'
+import { cache } from '../../src/middleware/cache/index.ts'
+
+Deno.test('Should return cached response', async () => {
+  const c = await caches.open('my-app')
+  await c.delete('http://localhost')
+
+  let oneTimeWord = 'Hello Hono'
+
+  const app = new Hono()
+  app.use(
+    '/',
+    cache({
+      cacheName: 'my-app',
+      wait: true,
+    })
+  )
+  app.get('/', (c) => {
+    const result = oneTimeWord
+    oneTimeWord = 'Not Found'
+    return c.text(result)
+  })
+
+  await app.request('http://localhost')
+  const res = await app.request('http://localhost')
+  expect(await res.text()).toBe('Hello Hono')
+  expect(res.headers.get('Hono-Cache-Expires')).toBeNull()
+  expect(res).not.toBeNull()
+  expect(res.status).toBe(200)
+  await c.delete('http://localhost')
+})
+
+Deno.test(
+  {
+    name: 'Should not return cached response over duration',
+    sanitizeResources: false,
+  },
+  async () => {
+    const time = new FakeTime()
+    const c = await caches.open('my-app')
+    await c.delete('http://localhost')
+
+    let oneTimeWord = 'Hello Hono'
+
+    const app = new Hono()
+    app.use(
+      '/',
+      cache({
+        cacheName: 'my-app',
+        wait: true,
+        duration: 60,
+      })
+    )
+    app.get('/', (c) => {
+      const result = oneTimeWord
+      oneTimeWord = 'Not Found'
+      return c.text(result)
+    })
+
+    await app.request('http://localhost')
+    let res = await app.request('http://localhost')
+
+    await time.tickAsync(59999)
+
+    expect(await res.text()).toBe('Hello Hono')
+    expect(res.headers.get('Hono-Cache-Expires')).toBeNull()
+    expect(res).not.toBeNull()
+    expect(res.status).toBe(200)
+
+    await time.tickAsync(1)
+
+    res = await app.request('http://localhost')
+    expect(await res.text()).toBe('Not Found')
+    expect(res.headers.get('Hono-Cache-Expires')).toBeNull()
+    expect(res).not.toBeNull()
+    expect(res.status).toBe(200)
+    await c.delete('http://localhost')
+  }
+)
+
+Deno.test(
+  {
+    name: 'Should return cached response if the response is immutable',
+    sanitizeResources: false,
+  },
+  async () => {
+    const c = await caches.open('my-app')
+    await c.delete('http://localhost')
+
+    let oneTime = true
+    let oneTimeWord = 'Hello Hono'
+
+    const example = new Hono()
+    example.get('/', (c) => {
+      const result = oneTimeWord
+      oneTimeWord = 'Not Found'
+      return c.text(result)
+    })
+
+    const app = new Hono()
+    app.use(
+      '/',
+      cache({
+        cacheName: 'my-app',
+        wait: true,
+      })
+    )
+    app.get('/', async (c) => {
+      const result = oneTime ? await fetch(`http://localhost:${server.addr.port}`) : 'Not Found'
+      oneTime = false
+      if (result instanceof Response) {
+        return result
+      } else {
+        return c.text('Not Found')
+      }
+    })
+
+    const server = Deno.serve({ port: 0 }, example.fetch)
+
+    await app.request('http://localhost')
+    const res = await app.request('http://localhost')
+    expect(await res.text()).toBe('Hello Hono')
+    expect(res.headers.get('Hono-Cache-Expires')).toBeNull()
+    expect(res).not.toBeNull()
+    expect(res.status).toBe(200)
+
+    await server.shutdown()
+    await c.delete('http://localhost')
+  }
+)
diff --git a/runtime-tests/deno/deno.json b/runtime_tests/deno/deno.json
similarity index 89%
rename from runtime-tests/deno/deno.json
rename to runtime_tests/deno/deno.json
index 240c5d2e4..012e7b7ee 100644
--- a/runtime-tests/deno/deno.json
+++ b/runtime_tests/deno/deno.json
@@ -13,6 +13,7 @@
   ],
   "imports": {
     "@std/assert": "jsr:@std/assert@^1.0.3",
+    "@std/expect": "jsr:@std/expect@^1.0.2",
     "@std/testing": "jsr:@std/testing@^1.0.1",
     "hono/jsx/jsx-runtime": "../../src/jsx/jsx-runtime.ts"
   }
diff --git a/runtime_tests/deno/deno.lock b/runtime_tests/deno/deno.lock
new file mode 100644
index 000000000..537fe7fe1
--- /dev/null
+++ b/runtime_tests/deno/deno.lock
@@ -0,0 +1,54 @@
+{
+  "version": "3",
+  "packages": {
+    "specifiers": {
+      "jsr:@std/assert@^1.0.3": "jsr:@std/assert@1.0.4",
+      "jsr:@std/assert@^1.0.4": "jsr:@std/assert@1.0.4",
+      "jsr:@std/async@^1.0.5": "jsr:@std/async@1.0.5",
+      "jsr:@std/data-structures@^1.0.2": "jsr:@std/data-structures@1.0.2",
+      "jsr:@std/expect@^1.0.2": "jsr:@std/expect@1.0.2",
+      "jsr:@std/internal@^1.0.3": "jsr:@std/internal@1.0.3",
+      "jsr:@std/testing@^1.0.1": "jsr:@std/testing@1.0.2"
+    },
+    "jsr": {
+      "@std/assert@1.0.4": {
+        "integrity": "d4c767ea578e5bc09c15b6e503376003e5b2d1f4c0cdf08524a92101ff4d7b96",
+        "dependencies": [
+          "jsr:@std/internal@^1.0.3"
+        ]
+      },
+      "@std/async@1.0.5": {
+        "integrity": "31d68214bfbb31bd4c6022401d484e3964147c76c9220098baa703a39b6c2da6"
+      },
+      "@std/data-structures@1.0.2": {
+        "integrity": "d586efced05ed91923514a192996d23673f32f695f7ebc37f0cc1e17928be600"
+      },
+      "@std/expect@1.0.2": {
+        "integrity": "37d5162eb1d30505e09f77f3fabbf6cde1e81ed0e72d2371cddbce1173eb86b4",
+        "dependencies": [
+          "jsr:@std/assert@^1.0.4",
+          "jsr:@std/internal@^1.0.3"
+        ]
+      },
+      "@std/internal@1.0.3": {
+        "integrity": "208e9b94a3d5649bd880e9ca38b885ab7651ab5b5303a56ed25de4755fb7b11e"
+      },
+      "@std/testing@1.0.2": {
+        "integrity": "9e8a7f4e26c219addabe7942d09c3450fa0a74e9662341961bc0ef502274dec3",
+        "dependencies": [
+          "jsr:@std/assert@^1.0.4",
+          "jsr:@std/async@^1.0.5",
+          "jsr:@std/data-structures@^1.0.2"
+        ]
+      }
+    }
+  },
+  "remote": {},
+  "workspace": {
+    "dependencies": [
+      "jsr:@std/assert@^1.0.3",
+      "jsr:@std/expect@^1.0.2",
+      "jsr:@std/testing@^1.0.1"
+    ]
+  }
+}
diff --git a/runtime-tests/deno/favicon.ico b/runtime_tests/deno/favicon.ico
similarity index 100%
rename from runtime-tests/deno/favicon.ico
rename to runtime_tests/deno/favicon.ico
diff --git a/runtime-tests/deno/hono.test.ts b/runtime_tests/deno/hono.test.ts
similarity index 100%
rename from runtime-tests/deno/hono.test.ts
rename to runtime_tests/deno/hono.test.ts
diff --git a/runtime-tests/deno/middleware.test.tsx b/runtime_tests/deno/middleware.test.tsx
similarity index 96%
rename from runtime-tests/deno/middleware.test.tsx
rename to runtime_tests/deno/middleware.test.tsx
index ed55dc80d..ad992fe9c 100644
--- a/runtime-tests/deno/middleware.test.tsx
+++ b/runtime_tests/deno/middleware.test.tsx
@@ -68,10 +68,10 @@ Deno.test('JSX middleware', async () => {
 Deno.test('Serve Static middleware', async () => {
   const app = new Hono()
   const onNotFound = spy(() => {})
-  app.all('/favicon.ico', serveStatic({ path: './runtime-tests/deno/favicon.ico' }))
+  app.all('/favicon.ico', serveStatic({ path: './runtime_tests/deno/favicon.ico' }))
   app.all(
     '/favicon-notfound.ico',
-    serveStatic({ path: './runtime-tests/deno/favicon-notfound.ico', onNotFound })
+    serveStatic({ path: './runtime_tests/deno/favicon-notfound.ico', onNotFound })
   )
   app.use('/favicon-notfound.ico', async (c, next) => {
     await next()
@@ -81,7 +81,7 @@ Deno.test('Serve Static middleware', async () => {
   app.get(
     '/static/*',
     serveStatic({
-      root: './runtime-tests/deno',
+      root: './runtime_tests/deno',
       onNotFound,
     })
   )
@@ -89,7 +89,7 @@ Deno.test('Serve Static middleware', async () => {
   app.get(
     '/dot-static/*',
     serveStatic({
-      root: './runtime-tests/deno',
+      root: './runtime_tests/deno',
       rewriteRequestPath: (path) => path.replace(/^\/dot-static/, './.static'),
     })
   )
diff --git a/runtime-tests/deno/ssg.test.tsx b/runtime_tests/deno/ssg.test.tsx
similarity index 100%
rename from runtime-tests/deno/ssg.test.tsx
rename to runtime_tests/deno/ssg.test.tsx
diff --git a/runtime-tests/deno/static/download b/runtime_tests/deno/static/download
similarity index 100%
rename from runtime-tests/deno/static/download
rename to runtime_tests/deno/static/download
diff --git a/runtime-tests/deno/static/hello.world/index.html b/runtime_tests/deno/static/hello.world/index.html
similarity index 100%
rename from runtime-tests/deno/static/hello.world/index.html
rename to runtime_tests/deno/static/hello.world/index.html
diff --git a/runtime-tests/deno/static/helloworld/index.html b/runtime_tests/deno/static/helloworld/index.html
similarity index 100%
rename from runtime-tests/deno/static/helloworld/index.html
rename to runtime_tests/deno/static/helloworld/index.html
diff --git a/runtime-tests/deno/static/plain.txt b/runtime_tests/deno/static/plain.txt
similarity index 100%
rename from runtime-tests/deno/static/plain.txt
rename to runtime_tests/deno/static/plain.txt
diff --git a/runtime-tests/deno/stream.test.ts b/runtime_tests/deno/stream.test.ts
similarity index 100%
rename from runtime-tests/deno/stream.test.ts
rename to runtime_tests/deno/stream.test.ts
diff --git a/runtime-tests/fastly/index.test.ts b/runtime_tests/fastly/index.test.ts
similarity index 100%
rename from runtime-tests/fastly/index.test.ts
rename to runtime_tests/fastly/index.test.ts
diff --git a/runtime-tests/fastly/vitest.config.ts b/runtime_tests/fastly/vitest.config.ts
similarity index 76%
rename from runtime-tests/fastly/vitest.config.ts
rename to runtime_tests/fastly/vitest.config.ts
index d01a1a004..c0480b139 100644
--- a/runtime-tests/fastly/vitest.config.ts
+++ b/runtime_tests/fastly/vitest.config.ts
@@ -7,8 +7,8 @@ export default defineConfig({
   plugins: [fastlyCompute()],
   test: {
     globals: true,
-    include: ['**/runtime-tests/fastly/**/(*.)+(test).+(ts|tsx)'],
-    exclude: ['**/runtime-tests/fastly/vitest.config.ts'],
+    include: ['**/runtime_tests/fastly/**/(*.)+(test).+(ts|tsx)'],
+    exclude: ['**/runtime_tests/fastly/vitest.config.ts'],
     coverage: {
       ...config.test?.coverage,
       reportsDirectory: './coverage/raw/runtime-fastly',
diff --git a/runtime-tests/lambda-edge/index.test.ts b/runtime_tests/lambda-edge/index.test.ts
similarity index 100%
rename from runtime-tests/lambda-edge/index.test.ts
rename to runtime_tests/lambda-edge/index.test.ts
diff --git a/runtime-tests/lambda-edge/vitest.config.ts b/runtime_tests/lambda-edge/vitest.config.ts
similarity index 72%
rename from runtime-tests/lambda-edge/vitest.config.ts
rename to runtime_tests/lambda-edge/vitest.config.ts
index 5fd8bc9fe..105ac9505 100644
--- a/runtime-tests/lambda-edge/vitest.config.ts
+++ b/runtime_tests/lambda-edge/vitest.config.ts
@@ -8,8 +8,8 @@ export default defineConfig({
       NAME: 'Node',
     },
     globals: true,
-    include: ['**/runtime-tests/lambda-edge/**/*.+(ts|tsx|js)'],
-    exclude: ['**/runtime-tests/lambda-edge/vitest.config.ts'],
+    include: ['**/runtime_tests/lambda-edge/**/*.+(ts|tsx|js)'],
+    exclude: ['**/runtime_tests/lambda-edge/vitest.config.ts'],
     coverage: {
       ...config.test?.coverage,
       reportsDirectory: './coverage/raw/runtime-lambda-edge',
diff --git a/runtime-tests/lambda/index.test.ts b/runtime_tests/lambda/index.test.ts
similarity index 100%
rename from runtime-tests/lambda/index.test.ts
rename to runtime_tests/lambda/index.test.ts
diff --git a/runtime-tests/lambda/mock.ts b/runtime_tests/lambda/mock.ts
similarity index 100%
rename from runtime-tests/lambda/mock.ts
rename to runtime_tests/lambda/mock.ts
diff --git a/runtime-tests/lambda/stream-mock.ts b/runtime_tests/lambda/stream-mock.ts
similarity index 100%
rename from runtime-tests/lambda/stream-mock.ts
rename to runtime_tests/lambda/stream-mock.ts
diff --git a/runtime-tests/lambda/stream.test.ts b/runtime_tests/lambda/stream.test.ts
similarity index 100%
rename from runtime-tests/lambda/stream.test.ts
rename to runtime_tests/lambda/stream.test.ts
diff --git a/runtime-tests/lambda/vitest.config.ts b/runtime_tests/lambda/vitest.config.ts
similarity index 64%
rename from runtime-tests/lambda/vitest.config.ts
rename to runtime_tests/lambda/vitest.config.ts
index 8cee5a8ec..01caae52b 100644
--- a/runtime-tests/lambda/vitest.config.ts
+++ b/runtime_tests/lambda/vitest.config.ts
@@ -8,11 +8,11 @@ export default defineConfig({
       NAME: 'Node',
     },
     globals: true,
-    include: ['**/runtime-tests/lambda/**/*.+(ts|tsx|js)'],
+    include: ['**/runtime_tests/lambda/**/*.+(ts|tsx|js)'],
     exclude: [
-      '**/runtime-tests/lambda/vitest.config.ts',
-      '**/runtime-tests/lambda/mock.ts',
-      '**/runtime-tests/lambda/stream-mock.ts',
+      '**/runtime_tests/lambda/vitest.config.ts',
+      '**/runtime_tests/lambda/mock.ts',
+      '**/runtime_tests/lambda/stream-mock.ts',
     ],
     coverage: {
       ...config.test?.coverage,
diff --git a/runtime-tests/node/index.test.ts b/runtime_tests/node/index.test.ts
similarity index 100%
rename from runtime-tests/node/index.test.ts
rename to runtime_tests/node/index.test.ts
diff --git a/runtime-tests/node/vitest.config.ts b/runtime_tests/node/vitest.config.ts
similarity index 74%
rename from runtime-tests/node/vitest.config.ts
rename to runtime_tests/node/vitest.config.ts
index 4cb6deed6..5387c11fd 100644
--- a/runtime-tests/node/vitest.config.ts
+++ b/runtime_tests/node/vitest.config.ts
@@ -8,8 +8,8 @@ export default defineConfig({
       NAME: 'Node',
     },
     globals: true,
-    include: ['**/runtime-tests/node/**/*.+(ts|tsx|js)'],
-    exclude: ['**/runtime-tests/node/vitest.config.ts'],
+    include: ['**/runtime_tests/node/**/*.+(ts|tsx|js)'],
+    exclude: ['**/runtime_tests/node/vitest.config.ts'],
     coverage: {
       ...config.test?.coverage,
       reportsDirectory: './coverage/raw/runtime-node',
diff --git a/runtime-tests/tsconfig.json b/runtime_tests/tsconfig.json
similarity index 100%
rename from runtime-tests/tsconfig.json
rename to runtime_tests/tsconfig.json
diff --git a/runtime-tests/workerd/index.test.ts b/runtime_tests/workerd/index.test.ts
similarity index 93%
rename from runtime-tests/workerd/index.test.ts
rename to runtime_tests/workerd/index.test.ts
index 2173ce6ae..8a28daa9d 100644
--- a/runtime-tests/workerd/index.test.ts
+++ b/runtime_tests/workerd/index.test.ts
@@ -6,7 +6,7 @@ describe('workerd', () => {
   let worker: UnstableDevWorker
 
   beforeAll(async () => {
-    worker = await unstable_dev('./runtime-tests/workerd/index.ts', {
+    worker = await unstable_dev('./runtime_tests/workerd/index.ts', {
       vars: {
         NAME: 'Hono',
       },
@@ -35,7 +35,7 @@ describe('workerd with WebSocket', () => {
   // worker.fetch does not support WebSocket:
   // https://github.com/cloudflare/workers-sdk/issues/4573#issuecomment-1850420973
   it('Should handle the WebSocket connection correctly', async () => {
-    const worker = await unstable_dev('./runtime-tests/workerd/index.ts', {
+    const worker = await unstable_dev('./runtime_tests/workerd/index.ts', {
       experimental: { disableExperimentalWarning: true },
     })
     const ws = new WebSocket(`ws://${worker.address}:${worker.port}/ws`)
diff --git a/runtime-tests/workerd/index.ts b/runtime_tests/workerd/index.ts
similarity index 100%
rename from runtime-tests/workerd/index.ts
rename to runtime_tests/workerd/index.ts
diff --git a/runtime-tests/workerd/vitest.config.ts b/runtime_tests/workerd/vitest.config.ts
similarity index 71%
rename from runtime-tests/workerd/vitest.config.ts
rename to runtime_tests/workerd/vitest.config.ts
index c82861be7..43410a1b4 100644
--- a/runtime-tests/workerd/vitest.config.ts
+++ b/runtime_tests/workerd/vitest.config.ts
@@ -5,8 +5,8 @@ import config from '../../vitest.config'
 export default defineConfig({
   test: {
     globals: true,
-    include: ['**/runtime-tests/workerd/**/(*.)+(test).+(ts|tsx)'],
-    exclude: ['**/runtime-tests/workerd/vitest.config.ts'],
+    include: ['**/runtime_tests/workerd/**/(*.)+(test).+(ts|tsx)'],
+    exclude: ['**/runtime_tests/workerd/vitest.config.ts'],
     coverage: {
       ...config.test?.coverage,
       reportsDirectory: './coverage/raw/runtime-workerd',
diff --git a/src/middleware/cache/index.ts b/src/middleware/cache/index.ts
index f7eecf6e4..749dfe463 100644
--- a/src/middleware/cache/index.ts
+++ b/src/middleware/cache/index.ts
@@ -16,6 +16,7 @@ import type { MiddlewareHandler } from '../../types'
  * @param {boolean} [options.wait=false] - A boolean indicating if Hono should wait for the Promise of the `cache.put` function to resolve before continuing with the request. Required to be true for the Deno environment.
  * @param {string} [options.cacheControl] - A string of directives for the `Cache-Control` header.
  * @param {string | string[]} [options.vary] - Sets the `Vary` header in the response. If the original response header already contains a `Vary` header, the values are merged, removing any duplicates.
+ * @param {number} [options.duration] - A number of seconds to cache the response.
  * @param {Function} [options.keyGenerator] - Generates keys for every request in the `cacheName` store. This can be used to cache data based on request parameters or context parameters.
  * @returns {MiddlewareHandler} The middleware handler function.
  * @throws {Error} If the `vary` option includes "*".
@@ -36,6 +37,7 @@ export const cache = (options: {
   wait?: boolean
   cacheControl?: string
   vary?: string | string[]
+  duration?: number
   keyGenerator?: (c: Context) => Promise<string> | string
 }): MiddlewareHandler => {
   if (!globalThis.caches) {
@@ -72,7 +74,9 @@ export const cache = (options: {
         let [name, value] = directive.trim().split('=', 2)
         name = name.toLowerCase()
         if (!existingDirectives.includes(name)) {
-          c.header('Cache-Control', `${name}${value ? `=${value}` : ''}`, { append: true })
+          c.header('Cache-Control', `${name}${value ? `=${value}` : ''}`, {
+            append: true,
+          })
         }
       }
     }
@@ -98,6 +102,27 @@ export const cache = (options: {
     }
   }
 
+  const internalCacheExpires = 'Hono-Cache-Expires'
+
+  // Create a new response for avoiding the immutable response.
+  const createNewResponse = (res: Response, callbackFn: (res: Response) => void): Response => {
+    try {
+      callbackFn(res)
+    } catch (e) {
+      if (e instanceof TypeError && e.message.includes('immutable')) {
+        // `res` is immutable (probably a response from a fetch API), so retry with a new response.
+        res = new Response(res.body, {
+          headers: res.headers,
+          status: res.status,
+        })
+        callbackFn(res)
+      } else {
+        throw e
+      }
+    }
+    return res
+  }
+
   return async function cache(c, next) {
     let key = c.req.url
     if (options.keyGenerator) {
@@ -109,7 +134,15 @@ export const cache = (options: {
     const cache = await caches.open(cacheName)
     const response = await cache.match(key)
     if (response) {
-      return new Response(response.body, response)
+      if (typeof options.duration === 'number') {
+        const expires = Number(response.headers.get(internalCacheExpires))
+        if (expires > Date.now()) {
+          const res = createNewResponse(response, (res) => res.headers.delete(internalCacheExpires))
+          return res
+        }
+      } else {
+        return response
+      }
     }
 
     await next()
@@ -117,7 +150,12 @@ export const cache = (options: {
       return
     }
     addHeader(c)
-    const res = c.res.clone()
+    let res = c.res.clone()
+
+    if (options.duration && options.duration > 0) {
+      const expiresTime = String(Date.now() + options.duration * 1000)
+      res = createNewResponse(res, (res) => res.headers.set(internalCacheExpires, expiresTime))
+    }
     if (options.wait) {
       await cache.put(key, res)
     } else {
diff --git a/src/middleware/serve-static/index.test.ts b/src/middleware/serve-static/index.test.ts
index 3f0c493f6..585008ca7 100644
--- a/src/middleware/serve-static/index.test.ts
+++ b/src/middleware/serve-static/index.test.ts
@@ -143,7 +143,6 @@ describe('Serve Static Middleware', () => {
     expect(res.status).toBe(200)
     expect(res.headers.get('Content-Encoding')).toBe('br')
     expect(res.headers.get('Vary')).toBe('Accept-Encoding')
-    expect(res.headers.get('Content-Type')).toBe('application/octet-stream')
     expect(await res.text()).toBe('Hello in static/hello.unknown.br')
   })
 
diff --git a/src/middleware/serve-static/index.ts b/src/middleware/serve-static/index.ts
index d9cdfbc06..6c45d61ac 100644
--- a/src/middleware/serve-static/index.ts
+++ b/src/middleware/serve-static/index.ts
@@ -99,8 +99,13 @@ export const serveStatic = <E extends Env = Env>(
     }
 
     if (content) {
-      const mimeType = (options.mimes && getMimeType(path, options.mimes)) || getMimeType(path)
-      c.header('Content-Type', mimeType || 'application/octet-stream')
+      const mimeType = options.mimes
+        ? getMimeType(path, options.mimes) ?? getMimeType(path)
+        : getMimeType(path)
+
+      if (mimeType) {
+        c.header('Content-Type', mimeType)
+      }
 
       if (options.precompressed && (!mimeType || COMPRESSIBLE_CONTENT_TYPE_REGEX.test(mimeType))) {
         const acceptEncodingSet = new Set(
diff --git a/vitest.config.ts b/vitest.config.ts
index 8c968fdee..26ce5de6d 100644
--- a/vitest.config.ts
+++ b/vitest.config.ts
@@ -19,7 +19,7 @@ export default defineConfig({
       exclude: [
         ...(configDefaults.coverage.exclude ?? []),
         'benchmarks',
-        'runtime-tests',
+        'runtime_tests',
         'build.ts',
         'src/test-utils',