diff --git a/crates/oxc_isolated_declarations/tests/deno.rs b/crates/oxc_isolated_declarations/tests/deno.rs
new file mode 100644
index 0000000000000..ff5f692528836
--- /dev/null
+++ b/crates/oxc_isolated_declarations/tests/deno.rs
@@ -0,0 +1,397 @@
+//! Copy from <https://github.com/denoland/deno_graph/blob/main/src/fast_check/transform_dts.rs#L932-#L1532>
+//! Make some changes to conform to the Isolated Declarations output
+
+#[cfg(test)]
+mod tests {
+    use oxc_allocator::Allocator;
+    use oxc_codegen::CodeGenerator;
+    use oxc_isolated_declarations::IsolatedDeclarations;
+    use oxc_parser::Parser;
+    use oxc_span::SourceType;
+
+    fn transform_dts_test(source: &str, expected: &str) {
+        let allocator = Allocator::default();
+        let source_type = SourceType::from_path("test.ts").unwrap();
+        let program = Parser::new(&allocator, source, source_type).parse().program;
+
+        let ret = IsolatedDeclarations::new(&allocator).build(&program);
+        let actual = CodeGenerator::new().build(&ret.program).source_text;
+        let expected_program = Parser::new(&allocator, expected, source_type).parse().program;
+        let expected = CodeGenerator::new().build(&expected_program).source_text;
+
+        assert_eq!(actual.trim(), expected.trim());
+    }
+
+    #[test]
+    fn dts_function_test() {
+        transform_dts_test(
+            "export function foo(a: number): number {
+  return {};
+}",
+            "export declare function foo(a: number): number;",
+        );
+        transform_dts_test(
+            "export function foo(a: string): number;
+export function foo(a: any): number {
+  return {};
+}",
+            "export declare function foo(a: string): number;",
+        );
+        transform_dts_test(
+            "export function foo(a = 2): number {
+  return 2;
+}",
+            "export declare function foo(a?: number): number;",
+        );
+        transform_dts_test(
+            "export function foo(a: string = 2): number {
+  return 2;
+}",
+            "export declare function foo(a?: string): number;",
+        );
+        // TODO: Isolated Declarations doesn't ObjectPattern
+        //         transform_dts_test(
+        //             "export function foo({a, b} = { a: 1, b: 2 }): number {
+        //   return 2;
+        // }",
+        //             "export declare function foo({ a, b }?: {
+        //   a: number;
+        //   b: number;
+        // }): number;",
+        //         );
+    }
+
+    #[test]
+    fn dts_class_decl_test() {
+        transform_dts_test(
+            "export class Foo {
+  a: number = 2;
+  static b: number = 1;
+  #b: number = 3;
+  constructor(value: string) {
+  return 42;
+  }
+  foo(): string {
+  return \"abc\";
+  }
+  #bar(): number {
+  return 2
+  }
+  get asdf(): number {
+
+  }
+  set asdf(value: number) {
+
+  }
+
+  static {
+
+  }
+}",
+            "export declare class Foo {
+  #private;
+  a: number;
+  static b: number;
+  constructor(value: string);
+  foo(): string;
+  get asdf(): number;
+  set asdf(value: number);
+}",
+        );
+    }
+
+    #[test]
+    fn dts_class_decl_rest_test() {
+        transform_dts_test(
+            "export class Foo {
+  constructor(...args: string[]) {}
+}",
+            "export declare class Foo {
+  constructor(...args: string[]);
+}",
+        );
+    }
+
+    #[test]
+    #[ignore = "Doesn't support class function overloads"]
+    fn dts_class_decl_overloads_test() {
+        transform_dts_test(
+            "export class Foo {
+  constructor(arg: string);
+  constructor(arg: number);
+  constructor(arg: any) {}
+}",
+            "export declare class Foo {
+  constructor(arg: string);
+  constructor(arg: number);
+}",
+        );
+
+        transform_dts_test(
+            "export class Foo {
+  foo(arg: string);
+  foo(arg: number);
+  foo(arg: any) {}
+}",
+            "export declare class Foo {
+  foo(arg: string);
+  foo(arg: number);
+}",
+        );
+
+        transform_dts_test(
+            "export class Foo {
+  constructor(arg: string);
+  constructor(arg: number);
+  constructor(arg: any) {}
+
+  bar(arg: number): number {
+  return 2
+  }
+
+  foo(arg: string);
+  foo(arg: number);
+  foo(arg: any) {}
+}",
+            "export declare class Foo {
+  constructor(arg: string);
+  constructor(arg: number);
+  bar(arg: number): number;
+  foo(arg: string);
+  foo(arg: number);
+}",
+        );
+    }
+
+    #[test]
+    fn dts_class_decl_prop_test() {
+        transform_dts_test(
+            "export class Foo { declare a: string }",
+            "export declare class Foo {
+  a: string;
+}",
+        );
+    }
+
+    #[test]
+    fn dts_class_decl_prop_infer_test() {
+        transform_dts_test(
+            "export class Foo { foo = (a: string): string => ({} as any) }",
+            "export declare class Foo {
+  foo: (a: string) => string;
+}",
+        );
+        transform_dts_test(
+            "export class Foo { foo = function(a: string): void {} }",
+            "export declare class Foo {
+  foo: (a: string) => void;
+}",
+        );
+    }
+
+    #[test]
+    fn dts_var_decl_test() {
+        transform_dts_test("export const foo: number = 42;", "export declare const foo: number;");
+
+        transform_dts_test("export var foo: number = 42;", "export declare var foo: number;");
+
+        transform_dts_test("export let foo: number = 42;", "export declare let foo: number;");
+    }
+
+    #[test]
+    fn dts_global_declare() {
+        transform_dts_test(
+            "declare global {
+  interface String {
+  fancyFormat(opts: StringFormatOptions): string;
+  }
+}",
+            "declare global {
+  interface String {
+  fancyFormat(opts: StringFormatOptions): string;
+  }
+}",
+        );
+    }
+
+    #[test]
+    fn dts_inference() {
+        transform_dts_test(
+            "export const foo = null as string as number;",
+            "export declare const foo: number;",
+        );
+    }
+
+    #[test]
+    fn dts_as_const() {
+        transform_dts_test(
+            "export const foo = [1, 2] as const;",
+            "export declare const foo: readonly [1, 2];",
+        );
+        transform_dts_test(
+            "export const foo = [1, ,2] as const;",
+            "export declare const foo: readonly [1, undefined, 2];",
+        );
+
+        transform_dts_test(
+      "export const foo = { str: \"bar\", bool: true, bool2: false, num: 42,   nullish: null } as const;",
+      "export declare const foo: {
+  readonly str: \"bar\";
+  readonly bool: true;
+  readonly bool2: false;
+  readonly num: 42;
+  readonly nullish: null;
+};",
+    );
+
+        transform_dts_test(
+            "export const foo = { str: [1, 2] as const } as const;",
+            "export declare const foo: {
+  readonly str: readonly [1, 2];
+};",
+        );
+    }
+
+    #[test]
+    fn dts_literal_inference_ann() {
+        transform_dts_test(
+            "export const foo: number = \"abc\";",
+            "export declare const foo: number;",
+        );
+        transform_dts_test("export let foo: number = \"abc\";", "export declare let foo: number;");
+        transform_dts_test("export var foo: number = \"abc\";", "export declare var foo: number;");
+    }
+
+    #[test]
+    fn dts_literal_inference() {
+        transform_dts_test("export const foo = 42;", "export declare const foo = 42;");
+        transform_dts_test("export const foo = \"foo\";", "export declare const foo = \"foo\";");
+        transform_dts_test("export const foo = true;", "export declare const foo: boolean;");
+        transform_dts_test("export const foo = false;", "export declare const foo: boolean;");
+        transform_dts_test("export const foo = null;", "export declare const foo: null;");
+        transform_dts_test("export let foo = undefined;", "export declare let foo: undefined;");
+        transform_dts_test("export let foo = 10n;", "export declare let foo: bigint;");
+    }
+
+    #[test]
+    fn dts_fn_expr() {
+        transform_dts_test(
+            "export let foo = function add(a: number, b: number): number {
+  return a + b;
+}",
+            "export declare let foo: (a: number, b: number) => number;",
+        );
+        transform_dts_test(
+            "export let foo = function add<T>([a, b]: T): void {}",
+            "export declare let foo: <T>([a, b]: T) => void;",
+        );
+        transform_dts_test(
+            "export let foo = function add<T>({a, b}: T): void {}",
+            "export declare let foo: <T>({ a, b }: T) => void;",
+        );
+        transform_dts_test(
+            "export let foo = function add(a = 2): void {}",
+            "export declare let foo: (a?: number) => void;",
+        );
+        transform_dts_test(
+            "export let foo = function add(...params: any[]): void {}",
+            "export declare let foo: (...params: any[]) => void;",
+        );
+    }
+
+    #[test]
+    fn dts_fn_arrow_expr() {
+        transform_dts_test(
+            "export let foo = (a: number, b: number): number => {
+  return a + b;
+}",
+            "export declare let foo: (a: number, b: number) => number;",
+        );
+        transform_dts_test(
+            "export let foo = <T>([a, b]: T): void => {}",
+            "export declare let foo: <T>([a, b]: T) => void;",
+        );
+        transform_dts_test(
+            "export let foo = <T>({a, b}: T): void => {}",
+            "export declare let foo: <T>({ a, b }: T) => void;",
+        );
+        transform_dts_test(
+            "export let foo = (a = 2): void => {}",
+            "export declare let foo: (a?: number) => void;",
+        );
+
+        transform_dts_test(
+            "export let foo = (...params: any[]): void => {}",
+            "export declare let foo: (...params: any[]) => void;",
+        );
+    }
+
+    #[test]
+    fn dts_type_export() {
+        transform_dts_test("interface Foo {}", "interface Foo {\n}");
+        transform_dts_test("type Foo = number;", "type Foo = number;");
+
+        transform_dts_test("export interface Foo {}", "export interface Foo {\n}");
+        transform_dts_test("export type Foo = number;", "export type Foo = number;");
+    }
+
+    #[test]
+    fn dts_enum_export() {
+        transform_dts_test(
+            "export enum Foo { A, B }",
+            "export declare enum Foo {\n  A=0,\n  B=1\n}",
+        );
+        transform_dts_test(
+            "export const enum Foo { A, B }",
+            "export declare const enum Foo {\n  A=0,\n  B=1\n}",
+        );
+
+        transform_dts_test(
+            "export enum Foo { A = \"foo\", B = \"bar\" }",
+            "export declare enum Foo {\n  A = \"foo\",\n  B = \"bar\"\n}",
+        );
+
+        // TODO: Enum rules https://www.typescriptlang.org/docs/handbook/enums.html
+    }
+
+    #[test]
+    fn dts_default_export() {
+        transform_dts_test(
+            "export default function(a: number, b: number): number {};",
+            "export default function(a: number, b: number): number;",
+        );
+        // TODO export default function overloads
+        //         transform_dts_test(
+        //             "export default function(a: number, b: number): number;
+        // export default function(a: number, b: number): any {
+        //   return foo
+        // };",
+        //             "export default function(a: number, b: number): number;",
+        //         );
+        transform_dts_test(
+            "export default class {foo = 2};",
+            "export default class {\n  foo: number;\n}",
+        );
+        transform_dts_test(
+            "export default 42;",
+            "declare const _default: number;\nexport default _default;",
+        );
+        transform_dts_test(
+            "const a: number = 42; export default a;",
+            "declare const a: number;\nexport default a;",
+        );
+    }
+
+    #[test]
+    fn dts_default_export_named() {
+        transform_dts_test(
+            "export { foo, bar } from \"foo\";",
+            "export { foo, bar } from \"foo\";",
+        );
+    }
+
+    #[test]
+    fn dts_default_export_all() {
+        transform_dts_test("export * as foo from \"foo\";", "export * as foo from \"foo\";");
+    }
+}
diff --git a/crates/oxc_isolated_declarations/tests/mod.rs b/crates/oxc_isolated_declarations/tests/mod.rs
index bf039e8120f5c..56ceacfe4a11a 100644
--- a/crates/oxc_isolated_declarations/tests/mod.rs
+++ b/crates/oxc_isolated_declarations/tests/mod.rs
@@ -1,3 +1,5 @@
+mod deno;
+
 use std::{fs, path::Path, sync::Arc};
 
 use oxc_allocator::Allocator;