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jest の toBe と toEqual の違いを比較

Posted at

1時間ほどハマったのでメモを。

toBe と toEqual の使い所

  • number, string の比較ならどちらでも良さそう。
  • object を比較する場合は、 toEqual 。

number, string

どちらも期待通りの結果に。

    it('number', () => {
      expect(1 + 1).toBe(2) // ok
      expect(1 + 1).toEqual(2) // ok
    })
    it('string', () => {
      expect('d' + 'b').toBe('db') // ok
      expect('d' + 'b').toEqual('db') // ok
    })

object

同じデータが入っていても toBe だと Fail します。

    it('object', () => {
      const user = { name: 'Hoge', age: 30 }
      // expect(user).toBe({ name: 'Hoge', age: 30 }) // Fail
      expect(user).toEqual({ name: 'Hoge', age: 30 })
    })

もともと日付の比較でハマってました。 Date は toEqual を利用しましょう。

    it('date', () => {
      const date = new Date('2020/01/01 00:00:00')
      // expect(date).toBe(new Date('2020/01/01 00:00:00')) // Fail
      expect(date).toEqual(new Date('2020/01/01 00:00:00'))
    })

new したインスタンスの比較も同様です。

    it('class', () => {
      class User {
        age: number
        constructor(age:number) {
          this.age = age
        }
      }
      const user = new User(30)
      // expect(user).toBe(new User(30)) // Fail
      expect(user).toEqual(new User(30))
    })

object の id が異なるからでしょうか。

参考

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