Populate result with new operator if new.target is defined

src/spy.ts

@@ -56,7 +56,9 @@ export function spy<A extends any[], R>(cb?: (...args: A) => R): SpyFn<A, R> {
     let type: 'ok' | 'error' = 'ok'
     if (fn.impl) {
       try {
-        result = fn.impl.apply(this, args)
+        result = new.target
+          ? new (fn.impl as any)(args)
+          : fn.impl.apply(this, args)
         type = 'ok'
       } catch (err: any) {
         result = err

test/index.test.ts

@@ -685,3 +685,21 @@ test('does not await on non-promise values that contain .then', async () => {
   const spiedResult = spied().addValue('Hello').addValue('World')
   expect(spiedResult).toStrictEqual(originalResult)
 })
+
+test('spyOn with new.target', () => {
+  const fn = {
+    fnFunc: () => {},
+    fnClass: class FnClass {},
+  }
+
+  spyOn(fn, 'fnFunc').willCall(function () {
+    expect(new.target).toBeUndefined()
+  })
+  spyOn(fn, 'fnClass').willCall(function () {
+    expect(new.target).toBeDefined()
+    return fn.fnClass
+  })
+
+  fn.fnFunc()
+  new fn.fnClass()
+})