diff --git a/src/dev/builder.ts b/src/dev/builder.ts
index bfa6c91f293..a32c4b5fa87 100644
--- a/src/dev/builder.ts
+++ b/src/dev/builder.ts
@@ -5,7 +5,6 @@ import {
   type ListenOptions,
   setBuildCache,
 } from "../app.ts";
-import { fsAdapter } from "../fs.ts";
 import * as path from "@std/path";
 import * as colors from "@std/fmt/colors";
 import { bundleJs } from "./esbuild.ts";
@@ -44,7 +43,7 @@ export interface FreshBuilder {
 }
 
 export class Builder implements FreshBuilder {
-  #transformer = new FreshFileTransformer(fsAdapter);
+  #transformer = new FreshFileTransformer();
   #addedInternalTransforms = false;
   #options: { target: string | string[] };
 
diff --git a/src/dev/file_transformer.ts b/src/dev/file_transformer.ts
index 190a54a4328..f9ad1fd0d4a 100644
--- a/src/dev/file_transformer.ts
+++ b/src/dev/file_transformer.ts
@@ -1,4 +1,3 @@
-import type { FsAdapter } from "../fs.ts";
 import { BUILD_ID } from "../runtime/build_id.ts";
 import { assetInternal } from "../runtime/shared_internal.tsx";
 
@@ -56,11 +55,6 @@ interface TransformReq {
 
 export class FreshFileTransformer {
   #transformers: Transformer[] = [];
-  #fs: FsAdapter;
-
-  constructor(fs: FsAdapter) {
-    this.#fs = fs;
-  }
 
   onTransform(options: OnTransformOptions, callback: TransformFn): void {
     this.#transformers.push({ options, fn: callback });
@@ -86,7 +80,7 @@ export class FreshFileTransformer {
 
     let content: Uint8Array;
     try {
-      content = await this.#fs.readFile(filePath);
+      content = await Deno.readFile(filePath);
     } catch (err) {
       if (err instanceof Deno.errors.NotFound) {
         return null;
diff --git a/src/dev/file_transformer_test.ts b/src/dev/file_transformer_test.ts
index e8537fa2f41..293c6a40555 100644
--- a/src/dev/file_transformer_test.ts
+++ b/src/dev/file_transformer_test.ts
@@ -1,27 +1,17 @@
 import { expect } from "@std/expect";
-import type { FsAdapter } from "../fs.ts";
 import {
   FreshFileTransformer,
   type ProcessedFile,
 } from "./file_transformer.ts";
 import { delay } from "../test_utils.ts";
+import { stub } from "@std/testing/mock";
 
-function testTransformer(files: Record<string, string>) {
-  const mockFs: FsAdapter = {
-    cwd: () => "/",
-    isDirectory: () => Promise.resolve(false),
-    mkdirp: () => Promise.resolve(),
-    walk: async function* foo() {
-    },
-    readFile: (file) => {
-      if (file instanceof URL) throw new Error("Not supported");
-      // deno-lint-ignore no-explicit-any
-      const content = (files as any)[file];
-      const buf = new TextEncoder().encode(content);
-      return Promise.resolve(buf);
-    },
-  };
-  return new FreshFileTransformer(mockFs);
+function stubDenoReadFile(content: string) {
+  return stub(Deno, "readFile", () => {
+    return Promise.resolve(
+      new TextEncoder().encode(content) as Uint8Array<ArrayBuffer>,
+    );
+  });
 }
 
 function consumeResult(result: ProcessedFile[]) {
@@ -52,9 +42,8 @@ function consumeResult(result: ProcessedFile[]) {
 }
 
 Deno.test("FileTransformer - transform sync", async () => {
-  const transformer = testTransformer({
-    "foo.txt": "foo",
-  });
+  const transformer = new FreshFileTransformer();
+  using _stub = stubDenoReadFile("foo");
 
   transformer.onTransform({ pluginName: "foo", filter: /.*/ }, (args) => {
     return {
@@ -70,9 +59,8 @@ Deno.test("FileTransformer - transform sync", async () => {
 });
 
 Deno.test("FileTransformer - transform async", async () => {
-  const transformer = testTransformer({
-    "foo.txt": "foo",
-  });
+  const transformer = new FreshFileTransformer();
+  using _stub = stubDenoReadFile("foo");
 
   transformer.onTransform({ pluginName: "foo", filter: /.*/ }, async (args) => {
     await delay(1);
@@ -89,9 +77,8 @@ Deno.test("FileTransformer - transform async", async () => {
 });
 
 Deno.test("FileTransformer - transform return Uint8Array", async () => {
-  const transformer = testTransformer({
-    "foo.txt": "foo",
-  });
+  const transformer = new FreshFileTransformer();
+  using _stub = stubDenoReadFile("foo");
 
   transformer.onTransform({ pluginName: "foo", filter: /.*/ }, () => {
     return {
@@ -107,9 +94,8 @@ Deno.test("FileTransformer - transform return Uint8Array", async () => {
 });
 
 Deno.test("FileTransformer - pass transformed content", async () => {
-  const transformer = testTransformer({
-    "input.txt": "input",
-  });
+  const transformer = new FreshFileTransformer();
+  using _stub = stubDenoReadFile("input");
 
   transformer.onTransform({ pluginName: "A", filter: /.*/ }, (args) => {
     return {
@@ -137,9 +123,8 @@ Deno.test("FileTransformer - pass transformed content", async () => {
 Deno.test(
   "FileTransformer - pass transformed content with multiple",
   async () => {
-    const transformer = testTransformer({
-      "input.txt": "input",
-    });
+    const transformer = new FreshFileTransformer();
+    using _stub = stubDenoReadFile("input");
 
     transformer.onTransform({ pluginName: "A", filter: /.*/ }, (args) => {
       return [{
@@ -167,9 +152,8 @@ Deno.test(
 );
 
 Deno.test("FileTransformer - return multiple results", async () => {
-  const transformer = testTransformer({
-    "foo.txt": "foo",
-  });
+  const transformer = new FreshFileTransformer();
+  using _stub = stubDenoReadFile("foo");
 
   const received: string[] = [];
   transformer.onTransform({ pluginName: "A", filter: /foo\.txt$/ }, () => {
@@ -197,9 +181,8 @@ Deno.test("FileTransformer - return multiple results", async () => {
 Deno.test(
   "FileTransformer - track input files through temporary results",
   async () => {
-    const transformer = testTransformer({
-      "foo.txt": "foo",
-    });
+    const transformer = new FreshFileTransformer();
+    using _stub = stubDenoReadFile("foo");
 
     transformer.onTransform({ pluginName: "A", filter: /foo\.txt$/ }, () => {
       return [{
diff --git a/src/fs.ts b/src/fs.ts
index 51a48ea455f..48216dff5e9 100644
--- a/src/fs.ts
+++ b/src/fs.ts
@@ -1,19 +1,16 @@
 import { walk, type WalkEntry, type WalkOptions } from "@std/fs/walk";
 
 export interface FsAdapter {
-  cwd(): string;
   walk(
     root: string | URL,
     options?: WalkOptions,
   ): AsyncIterableIterator<WalkEntry>;
   isDirectory(path: string | URL): Promise<boolean>;
   mkdirp(dir: string): Promise<void>;
-  readFile(path: string | URL): Promise<Uint8Array>;
 }
 
 export const fsAdapter: FsAdapter = {
   walk,
-  cwd: Deno.cwd,
   async isDirectory(path) {
     try {
       const stat = await Deno.stat(path);
@@ -32,5 +29,4 @@ export const fsAdapter: FsAdapter = {
       }
     }
   },
-  readFile: Deno.readFile,
 };
diff --git a/src/plugins/fs_routes/mod.ts b/src/plugins/fs_routes/mod.ts
index 9a7c985587b..35d6d7c0970 100644
--- a/src/plugins/fs_routes/mod.ts
+++ b/src/plugins/fs_routes/mod.ts
@@ -72,7 +72,7 @@ export async function fsRoutes<State>(
   const fs = options._fs ?? fsAdapter;
 
   const dir = options.dir
-    ? parseRootPath(options.dir, fs.cwd())
+    ? parseRootPath(options.dir, Deno.cwd())
     : app.config.root;
   const islandDir = path.join(dir, "islands");
   const routesDir = path.join(dir, "routes");
diff --git a/src/plugins/fs_routes/mod_test.tsx b/src/plugins/fs_routes/mod_test.tsx
index c1e957b4a4e..d1f872a8f92 100644
--- a/src/plugins/fs_routes/mod_test.tsx
+++ b/src/plugins/fs_routes/mod_test.tsx
@@ -13,11 +13,13 @@ import { type HandlerByMethod, type HandlerFn, page } from "../../handlers.ts";
 import type { Method } from "../../router.ts";
 import { parseHtml } from "../../../tests/test_utils.tsx";
 import type { FreshContext } from "fresh";
+import { stub } from "@std/testing/mock";
 
 async function createServer<T>(
   files: Record<string, string | Uint8Array | FreshFsItem<T>>,
 ): Promise<FakeServer> {
   const app = new App<T>();
+  using _stub = stub(Deno, "cwd", () => ".");
 
   await fsRoutes(
     app,
diff --git a/src/test_utils.ts b/src/test_utils.ts
index 68e678cc0f8..e525aeb769b 100644
--- a/src/test_utils.ts
+++ b/src/test_utils.ts
@@ -92,7 +92,6 @@ export function serveMiddleware<T>(
 
 export function createFakeFs(files: Record<string, unknown>): FsAdapter {
   return {
-    cwd: () => ".",
     async *walk(_root) {
       // FIXME: ignore
       for (const file of Object.keys(files)) {
@@ -112,7 +111,6 @@ export function createFakeFs(files: Record<string, unknown>): FsAdapter {
     },
     async mkdirp(_dir: string) {
     },
-    readFile: Deno.readFile,
   };
 }