fix(spy): don't fail when spying on static getters (#8589)

Author: sheremet-va

packages/spy/src/index.ts

@@ -264,7 +264,11 @@ export function spyOn<T extends object, K extends keyof T>(
   const originalType = typeof originalImplementation
 
   assert(
-    originalType === 'function',
+    // allow only functions
+    originalType === 'function'
+    // or allow getter/setter on a static value,
+    // e.g. spyOn({ value: 3 }, 'value', 'get')
+    || (accessType !== 'value' && original == null),
     `vi.spyOn() can only spy on a function. Received ${originalType}.`,
   )
 

test/core/test/mocking/vi-spyOn.test.ts

@@ -282,6 +282,30 @@ describe('vi.spyOn() settings', () => {
     expect(spy2.mock.calls).toEqual(spy1.mock.calls)
   })
 
+  test('vi.spyOn() when spying on a static getter spy returns the same spy', () => {
+    const object = createObject()
+    const spy1 = vi.spyOn(object, 'static', 'get')
+    const spy2 = vi.spyOn(object, 'static', 'get')
+    expect(spy1).toBe(spy2)
+
+    const _example = object.static
+    expect(spy2).toHaveBeenCalledTimes(1)
+    expect(spy1).toHaveBeenCalledTimes(1)
+    expect(spy2.mock.calls).toEqual(spy1.mock.calls)
+  })
+
+  test('vi.spyOn() when spying on a static setter spy returns the same spy', () => {
+    const object = createObject()
+    const spy1 = vi.spyOn(object, 'static', 'set')
+    const spy2 = vi.spyOn(object, 'static', 'set')
+    expect(spy1).toBe(spy2)
+
+    object.static = 33
+    expect(spy2).toHaveBeenCalledTimes(1)
+    expect(spy1).toHaveBeenCalledTimes(1)
+    expect(spy2.mock.calls).toEqual(spy1.mock.calls)
+  })
+
   test('vi.spyOn() can spy on multiple class instances without intervention', () => {
     class Example {
       method() {
@@ -668,5 +692,6 @@ function createObject() {
     set getter(value: number) {
       getterValue = value
     },
+    static: 42,
   }
 }