diff --git a/README.md b/README.md
index 8b0d95c..c40cc08 100644
--- a/README.md
+++ b/README.md
@@ -61,7 +61,7 @@ const mod = await loadFile("config.js");
 
 mod.exports.default.foo.push("b");
 
-await writeFile(mod);
+await writeFile(mod, "config.js");
 ```
 
 Updated `config.js`:
@@ -164,7 +164,7 @@ function updateConfig() {
 We also experiment to provide a few high level helpers to make common tasks easier. You could import them from `magicast/helpers`. They might be moved to a separate package in the future.
 
 ```js
-import { 
+import {
   deepMergeObject,
   addNuxtModule,
   addVitePlugin,
diff --git a/src/code.ts b/src/code.ts
index e030d7a..76ed658 100644
--- a/src/code.ts
+++ b/src/code.ts
@@ -77,13 +77,12 @@ export async function loadFile<Exports extends object = any>(
 }
 
 export async function writeFile(
-  node: { ast: ASTNode } | ASTNode,
-  filename?: string,
+  node: { $ast: ASTNode } | ASTNode,
+  filename: string,
   options?: ParseOptions,
 ): Promise<void> {
-  const ast = "ast" in node ? node.ast : node;
+  const ast = "$ast" in node ? node.$ast : node;
   const { code, map } = generateCode(ast, options);
-  filename = filename || (ast as any).name || "output.js";
   await fsp.writeFile(filename as string, code);
   if (map) {
     await fsp.writeFile(filename + ".map", map);
diff --git a/src/types.ts b/src/types.ts
index ab40c3c..a4e3b31 100644
--- a/src/types.ts
+++ b/src/types.ts
@@ -20,7 +20,6 @@ export interface Token {
 export interface ParsedFileNode {
   type: "file";
   program: Program;
-  name?: string;
   loc: Loc;
   comments: null | any;
 }
diff --git a/test/code.test.ts b/test/code.test.ts
new file mode 100644
index 0000000..a771669
--- /dev/null
+++ b/test/code.test.ts
@@ -0,0 +1,50 @@
+import { promises as fsp } from "node:fs";
+import { describe, expect, it } from "vitest";
+import { loadFile, parseModule, writeFile } from "../src";
+
+describe("code", () => {
+  it("should load and parse a file", async () => {
+    const stub = await loadFile("./test/stubs/config.ts");
+
+    expect(stub).toBeDefined();
+    expect(stub.$type).toBe("module");
+    expect(stub.$ast).toBeDefined();
+
+    expect(stub.$code).toMatchInlineSnapshot(`
+    "export default {
+      foo: [\\"a\\"],
+    };
+    "`);
+
+    const mod = parseModule(
+      `
+    export default {
+      foo: ["a"],
+    };
+    `,
+      { sourceFileName: "./test/stubs/config.ts" },
+    );
+
+    expect(stub.exports).toEqual(mod.exports);
+  });
+
+  it("should write file from a module", async () => {
+    const mod = parseModule(
+      `
+    export default {
+      foo: ["a"],
+    };
+    `,
+      { sourceFileName: "./test/stubs/config.ts" },
+    );
+
+    await writeFile(mod, "./test/stubs/config2.ts");
+
+    const stub = await fsp.readFile("./test/stubs/config2.ts", "utf8");
+
+    expect(stub).toMatchInlineSnapshot(`
+    "export default {
+      foo: [\\"a\\"],
+    };"`);
+  });
+});
diff --git a/test/stubs/.gitignore b/test/stubs/.gitignore
new file mode 100644
index 0000000..38988bb
--- /dev/null
+++ b/test/stubs/.gitignore
@@ -0,0 +1 @@
+config2.ts
diff --git a/test/stubs/config.ts b/test/stubs/config.ts
new file mode 100644
index 0000000..f9dde13
--- /dev/null
+++ b/test/stubs/config.ts
@@ -0,0 +1,3 @@
+export default {
+  foo: ["a"],
+};