fix: update spy type inference (#643)

* fix: update spy type inference

* test: add test case for `spyOn` type inference

* refactor: merge overload declarations

* chore: remove unused parameter

* test: use `happy-dom`

* test: skip flaky test

Co-authored-by: Ivan Demchuk <ivan.demchuk@gmail.com>

packages/vitest/src/integrations/jest-mock.ts

@@ -117,17 +117,10 @@ export function spyOn<T, G extends Properties<Required<T>>>(
   methodName: G,
   accesType: 'set',
 ): SpyInstance<[T[G]], void>
-export function spyOn<T, M extends Classes<Required<T>>>(
-  object: T,
-  method: M
-): Required<T>[M] extends new (...args: infer A) => infer R
-  ? SpyInstance<A, R>
-  : never
-export function spyOn<T, M extends Methods<Required<T>>>(
+export function spyOn<T, M extends (Methods<Required<T>> | Classes<Required<T>>)>(
   obj: T,
   methodName: M,
-  mock?: T[M]
-): Required<T>[M] extends (...args: infer A) => infer R ? SpyInstance<A, R> : never
+): Required<T>[M] extends (...args: infer A) => infer R | (new (...args: infer A) => infer R) ? SpyInstance<A, R> : never
 export function spyOn<T, K extends keyof T>(
   obj: T,
   method: K,

test/core/test/spy.test.ts

@@ -0,0 +1,12 @@
+import { describe, expect, spyOn, test } from 'vitest'
+
+/**
+ * @vitest-environment happy-dom
+ */
+
+describe('spyOn', () => {
+  test('correctly infers method types', async() => {
+    spyOn(localStorage, 'getItem').mockReturnValue('world')
+    expect(window.localStorage.getItem('hello')).toEqual('world')
+  })
+})