fix(spy): mockReturnValue with class mocks

packages/spy/src/index.ts

@@ -121,11 +121,17 @@ export function createMockInstance(options: MockInstanceOption = {}): Mock<Proce
   }
 
   mock.mockReturnValue = function mockReturnValue(value) {
-    return mock.mockImplementation(() => value)
+    // eslint-disable-next-line prefer-arrow-callback
+    return mock.mockImplementation(function () {
+      return value
+    })
   }
 
   mock.mockReturnValueOnce = function mockReturnValueOnce(value) {
-    return mock.mockImplementationOnce(() => value)
+    // eslint-disable-next-line prefer-arrow-callback
+    return mock.mockImplementationOnce(function () {
+      return value
+    })
   }
 
   mock.mockResolvedValue = function mockResolvedValue(value) {

packages/spy/src/types.ts

@@ -47,7 +47,7 @@ export type MockParameters<T extends Procedure | Constructable> = T extends Cons
     ? Parameters<T> : never
 
 export type MockReturnType<T extends Procedure | Constructable> = T extends Constructable
-  ? void
+  ? InstanceType<T>
   : T extends Procedure
     ? ReturnType<T> : never
 

test/core/test/mocking/vi-fn.test-d.ts

@@ -17,11 +17,11 @@ test('spy.mock when implementation is a class', () => {
   const Mock = vi.fn(Klass)
 
   expectTypeOf(Mock.mock.calls).toEqualTypeOf<[a: string, b?: number][]>()
-  expectTypeOf(Mock.mock.results).toEqualTypeOf<MockResult<void>[]>()
+  expectTypeOf(Mock.mock.results).toEqualTypeOf<MockResult<Klass>[]>()
   expectTypeOf(Mock.mock.contexts).toEqualTypeOf<Klass[]>()
   expectTypeOf(Mock.mock.instances).toEqualTypeOf<Klass[]>()
   expectTypeOf(Mock.mock.invocationCallOrder).toEqualTypeOf<number[]>()
-  expectTypeOf(Mock.mock.settledResults).toEqualTypeOf<MockSettledResult<void>[]>()
+  expectTypeOf(Mock.mock.settledResults).toEqualTypeOf<MockSettledResult<Klass>[]>()
   expectTypeOf(Mock.mock.lastCall).toEqualTypeOf<[a: string, b?: number] | undefined>()
 
   // static properties are defined

test/core/test/spy.test.ts

@@ -30,4 +30,11 @@ describe('spyOn', () => {
 
     expect(hw.hello()).toEqual('hello world')
   })
+
+  test('mock return value for constructor', () => {
+    vi.spyOn(mock, 'HelloWorld').mockReturnValueOnce({ hello: () => 'hello world' })
+
+    const mockedHelloWorld = new mock.HelloWorld()
+    expect(mockedHelloWorld.hello()).toEqual('hello world')
+  })
 })