test(store): add unit tests for shallow equality utility

packages/store/tests/shallow.test.ts

@@ -0,0 +1,84 @@
+import { describe, expect, test } from 'vitest'
+import { shallow } from '../src/shallow'
+
+describe('shallow', () => {
+  test('returns true for identical primitives and references', () => {
+    expect(shallow(1, 1)).toBe(true)
+    expect(shallow('test', 'test')).toBe(true)
+    expect(shallow(true, true)).toBe(true)
+    expect(shallow(null, null)).toBe(true)
+    expect(shallow(undefined, undefined)).toBe(true)
+    expect(shallow(NaN, NaN)).toBe(true)
+
+    const obj = { a: 1 }
+    expect(shallow(obj, obj)).toBe(true)
+  })
+
+  test('returns false for mismatched primitives and null/objects', () => {
+    expect(shallow(1, 2)).toBe(false)
+    expect(shallow('a', 'b')).toBe(false)
+    expect(shallow(null, {})).toBe(false)
+    expect(shallow({}, null)).toBe(false)
+    expect(shallow(undefined, {})).toBe(false)
+    expect(shallow(1 as any, {})).toBe(false)
+  })
+
+  test('compares shallow objects correctly', () => {
+    expect(shallow({ a: 1, b: '2' }, { a: 1, b: '2' })).toBe(true)
+    expect(shallow({ a: 1, b: '2' }, { a: 1, b: '3' })).toBe(false)
+    expect(shallow({ a: 1 }, { a: 1, b: 2 })).toBe(false)
+    expect(shallow({ a: 1, b: 2 }, { a: 1 })).toBe(false)
+  })
+
+  test('compares objects with symbol keys', () => {
+    const sym = Symbol('key')
+    expect(shallow({ [sym]: 1, a: 2 }, { [sym]: 1, a: 2 })).toBe(true)
+    expect(shallow({ [sym]: 1, a: 2 }, { [sym]: 2, a: 2 })).toBe(false)
+  })
+
+  test('compares arrays shallowly', () => {
+    expect(shallow([1, 2, 3], [1, 2, 3])).toBe(true)
+    expect(shallow([1, 2, 3], [1, 2, 4])).toBe(false)
+    expect(shallow([1, 2], [1, 2, 3])).toBe(false)
+  })
+
+  test('compares Map instances', () => {
+    const mapA = new Map<string, number>([
+      ['a', 1],
+      ['b', 2],
+    ])
+    const mapB = new Map<string, number>([
+      ['a', 1],
+      ['b', 2],
+    ])
+    const mapC = new Map<string, number>([
+      ['a', 1],
+      ['b', 3],
+    ])
+    const mapD = new Map<string, number>([['a', 1]])
+
+    expect(shallow(mapA, mapB)).toBe(true)
+    expect(shallow(mapA, mapC)).toBe(false)
+    expect(shallow(mapA, mapD)).toBe(false)
+  })
+
+  test('compares Set instances', () => {
+    const setA = new Set([1, 2, 3])
+    const setB = new Set([1, 2, 3])
+    const setC = new Set([1, 2, 4])
+    const setD = new Set([1, 2])
+
+    expect(shallow(setA, setB)).toBe(true)
+    expect(shallow(setA, setC)).toBe(false)
+    expect(shallow(setA, setD)).toBe(false)
+  })
+
+  test('compares Date instances', () => {
+    const d1 = new Date('2026-01-01T00:00:00.000Z')
+    const d2 = new Date('2026-01-01T00:00:00.000Z')
+    const d3 = new Date('2026-01-02T00:00:00.000Z')
+
+    expect(shallow(d1, d2)).toBe(true)
+    expect(shallow(d1, d3)).toBe(false)
+  })
+})