From 1e17308674f917ac05e0dccb10121b356e748e24 Mon Sep 17 00:00:00 2001
From: Samuel <samuel.souto7@gmail.com>
Date: Fri, 30 Dec 2022 17:15:06 -0300
Subject: [PATCH 1/2] Fixing type issue with spyOn method

---
 packages/vitest/src/integrations/spy.ts | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/packages/vitest/src/integrations/spy.ts b/packages/vitest/src/integrations/spy.ts
index b83d2c9a0f63..6a57cf60a357 100644
--- a/packages/vitest/src/integrations/spy.ts
+++ b/packages/vitest/src/integrations/spy.ts
@@ -154,10 +154,10 @@ export function spyOn<T, G extends Properties<Required<T>>>(
   methodName: G,
   accessType: 'set',
 ): SpyInstance<[T[G]], void>
-export function spyOn<T, M extends (Methods<Required<T>> | Classes<Required<T>>)>(
+export function spyOn<T, M extends (Classes<Required<T>> | Methods<Required<T>>)>(
   obj: T,
   methodName: M,
-): Required<T>[M] extends (...args: infer A) => infer R | (new (...args: infer A) => infer R) ? SpyInstance<A, R> : never
+): Required<T>[M] extends ({ new (...args: infer A): infer R }) | ((...args: infer A) => infer R) ? SpyInstance<A, R> : never
 export function spyOn<T, K extends keyof T>(
   obj: T,
   method: K,

From fa8c63175582c58c462cebc4ccda7828f664feda Mon Sep 17 00:00:00 2001
From: Samuel <samuel.souto7@gmail.com>
Date: Mon, 2 Jan 2023 15:10:46 -0300
Subject: [PATCH 2/2] Adding tests

---
 test/core/test/fixtures/hello-mock.ts |  5 +++++
 test/core/test/spy.test.ts            | 20 ++++++++++++++++++++
 2 files changed, 25 insertions(+)
 create mode 100644 test/core/test/fixtures/hello-mock.ts

diff --git a/test/core/test/fixtures/hello-mock.ts b/test/core/test/fixtures/hello-mock.ts
new file mode 100644
index 000000000000..805866f4b568
--- /dev/null
+++ b/test/core/test/fixtures/hello-mock.ts
@@ -0,0 +1,5 @@
+export class HelloWorld {
+  hello() {
+    return 'Hello World!'
+  }
+}
diff --git a/test/core/test/spy.test.ts b/test/core/test/spy.test.ts
index 140cbd1eef77..35cddb90374a 100644
--- a/test/core/test/spy.test.ts
+++ b/test/core/test/spy.test.ts
@@ -1,12 +1,32 @@
 import { describe, expect, test, vi } from 'vitest'
+import * as mock from './fixtures/hello-mock'
 
 /**
  * @vitest-environment happy-dom
  */
 
 describe('spyOn', () => {
+  const hw = new mock.HelloWorld()
+
   test('correctly infers method types', async () => {
     vi.spyOn(localStorage, 'getItem').mockReturnValue('world')
     expect(window.localStorage.getItem('hello')).toEqual('world')
   })
+
+  test('infers a class correctly', () => {
+    vi.spyOn(mock, 'HelloWorld').mockImplementationOnce(() => {
+      const Mock = vi.fn()
+      Mock.prototype.hello = vi.fn(() => 'hello world')
+      return new Mock()
+    })
+
+    const mockedHelloWorld = new mock.HelloWorld()
+    expect(mockedHelloWorld.hello()).toEqual('hello world')
+  })
+
+  test('infers a method correctly', () => {
+    vi.spyOn(hw, 'hello').mockImplementationOnce(() => 'hello world')
+
+    expect(hw.hello()).toEqual('hello world')
+  })
 })