✅ test: add unit test for atomWithReset utility

tests/vanilla/utils/atomWithReset.test.ts

@@ -0,0 +1,56 @@
+import { beforeEach, describe, expect, it, vi } from 'vitest'
+import { createStore } from 'jotai/vanilla'
+import { RESET, atomWithReset } from 'jotai/vanilla/utils'
+
+describe('atomWithReset', () => {
+  let initialValue: number
+  let testAtom: any
+
+  beforeEach(() => {
+    vi.clearAllMocks()
+    initialValue = 10
+    testAtom = atomWithReset(initialValue)
+  })
+
+  it('should create an atom with initial value', () => {
+    const { init } = testAtom
+    expect(init).toBe(initialValue)
+  })
+
+  it('should reset to initial value using RESET', () => {
+    const store = createStore()
+    store.set(testAtom, 123)
+    store.set(testAtom, RESET)
+    expect(store.get(testAtom)).toBe(initialValue)
+
+    const set = vi.fn()
+    const get = vi.fn(() => 20)
+    testAtom.write(get, set, RESET)
+    expect(set).toHaveBeenCalledWith(testAtom, initialValue)
+  })
+
+  it('should update atom with a new value', () => {
+    const store = createStore()
+    store.set(testAtom, 123)
+    store.set(testAtom, 30)
+    expect(store.get(testAtom)).toBe(30)
+
+    const set = vi.fn()
+    const get = vi.fn(() => 20)
+    testAtom.write(get, set, 30)
+    expect(set).toHaveBeenCalledWith(testAtom, 30)
+  })
+
+  it('should update atom using a function', () => {
+    const store = createStore()
+    store.set(testAtom, 123)
+    store.set(testAtom, (prev: number) => prev + 10)
+    expect(store.get(testAtom)).toBe(133)
+
+    const set = vi.fn()
+    const get = vi.fn(() => 20)
+    const updateFn = (prev: number) => prev + 10
+    testAtom.write(get, set, updateFn)
+    expect(set).toHaveBeenCalledWith(testAtom, 30)
+  })
+})