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Merged
pull merged 1 commit into from
Jan 23, 2026
Merged

[pull] main from vitest-dev:main #262

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6 changes: 6 additions & 0 deletions packages/spy/src/index.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -263,6 +263,12 @@ export function spyOn<T extends object, K extends keyof T>(

if (originalDescriptor) {
original = originalDescriptor[accessType]
// weird Proxy edge case where descriptor's value is undefined,
// but there's still a value on the object when called
// https://github.com/vitest-dev/vitest/issues/9439
if (original == null && accessType === 'value') {
original = object[key] as unknown as Procedure
}
}
else if (accessType !== 'value') {
original = () => object[key]
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108 changes: 66 additions & 42 deletions test/core/test/mocking/vi-spyOn.test.ts
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Original file line number Diff line number Diff line change
@@ -1,61 +1,85 @@
import type { MockContext } from 'vitest'
import { describe, expect, test, vi } from 'vitest'

test('vi.fn() has correct length', () => {
const fn0 = vi.spyOn({ fn: () => {} }, 'fn')
expect(fn0.length).toBe(0)
describe('vi.spyOn() edge cases', () => {
test('vi.spyOn() has correct length', () => {
const fn0 = vi.spyOn({ fn: () => {} }, 'fn')
expect(fn0.length).toBe(0)

const fnArgs = vi.spyOn({ fn: (..._args: any[]) => {} }, 'fn')
expect(fnArgs.length).toBe(0)
const fnArgs = vi.spyOn({ fn: (..._args: any[]) => {} }, 'fn')
expect(fnArgs.length).toBe(0)

const fn1 = vi.spyOn({ fn: (_arg1: any) => {} }, 'fn')
expect(fn1.length).toBe(1)
const fn1 = vi.spyOn({ fn: (_arg1: any) => {} }, 'fn')
expect(fn1.length).toBe(1)

const fn2 = vi.spyOn({ fn: (_arg1: any, _arg2: any) => {} }, 'fn')
expect(fn2.length).toBe(2)
const fn2 = vi.spyOn({ fn: (_arg1: any, _arg2: any) => {} }, 'fn')
expect(fn2.length).toBe(2)

const fn3 = vi.spyOn({ fn: (_arg1: any, _arg2: any, _arg3: any) => {} }, 'fn')
expect(fn3.length).toBe(3)
})
const fn3 = vi.spyOn({ fn: (_arg1: any, _arg2: any, _arg3: any) => {} }, 'fn')
expect(fn3.length).toBe(3)
})

describe('vi.spyOn() copies static properties', () => {
test('vi.spyOn() copies properties from functions', () => {
function a() {}
a.HELLO_WORLD = true
const obj = {
a,
}
test('can spy on a proxy with undefined descriptor\'s value', () => {
const obj = new Proxy<{ fn: () => number }>({} as any, {
get(_, prop) {
if (prop === 'fn') {
return () => 42
}
},
getOwnPropertyDescriptor(_, prop) {
if (prop === 'fn') {
return {
configurable: true,
enumerable: true,
value: undefined,
writable: true,
}
}
},
})
const spy = vi.spyOn(obj, 'fn')
expect(spy()).toBe(42)
})

const spy = vi.spyOn(obj, 'a')
describe('vi.spyOn() copies static properties', () => {
test('vi.spyOn() copies properties from functions', () => {
function a() {}
a.HELLO_WORLD = true
const obj = {
a,
}

expect(obj.a.HELLO_WORLD).toBe(true)
expect(spy.HELLO_WORLD).toBe(true)
})
const spy = vi.spyOn(obj, 'a')

test('vi.spyOn() copies properties from classes', () => {
class A {
static HELLO_WORLD = true
}
const obj = {
A,
}
expect(obj.a.HELLO_WORLD).toBe(true)
expect(spy.HELLO_WORLD).toBe(true)
})

const spy = vi.spyOn(obj, 'A')
test('vi.spyOn() copies properties from classes', () => {
class A {
static HELLO_WORLD = true
}
const obj = {
A,
}

expect(obj.A.HELLO_WORLD).toBe(true)
expect(spy.HELLO_WORLD).toBe(true)
})
const spy = vi.spyOn(obj, 'A')

test('vi.spyOn() ignores node.js.promisify symbol', () => {
const promisifySymbol = Symbol.for('nodejs.util.promisify.custom')
class Example {
static [promisifySymbol] = () => Promise.resolve(42)
}
const obj = { Example }
expect(obj.A.HELLO_WORLD).toBe(true)
expect(spy.HELLO_WORLD).toBe(true)
})

const spy = vi.spyOn(obj, 'Example')
test('vi.spyOn() ignores node.js.promisify symbol', () => {
const promisifySymbol = Symbol.for('nodejs.util.promisify.custom')
class Example {
static [promisifySymbol] = () => Promise.resolve(42)
}
const obj = { Example }

expect(spy[promisifySymbol]).toBe(undefined)
const spy = vi.spyOn(obj, 'Example')

expect(spy[promisifySymbol]).toBe(undefined)
})
})
})

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