Jest - 在 describe 块中导入多个测试，重用 beforeEach() 中定义的变量

Question

我熟悉 RSpec，通过编写共享示例可以很容易地重用测试用例

shared_example_for 'a cute pet' do 
  it 'tests that the pet is a small' { expect(pet.size).to be_lesser_than(10) }
  it 'tests that the pet can smile' { expect(pet.can_smile?).to be }
end

describe 'The Octocat' do
  let(:pet) { Octocat.new }

  it_behaves_like 'a cute pet'
end
...
describe 'The Doge' do 
  let(:pet) { Doge.new }

  it_behaves_like 'a cute pet'
end

在 Jest 中有等价物吗？ 能让我重用在 beforeEach() 块中设置的变量的东西？ 我正在尝试找到一种使用以下内容的方法：

# __tests__/cuteness.js
export const cutenessTests = function() {
  test('it is small', () => {
    expect(petSetInBefore.length).toBeLesserThan(5)
  })
  test('it can smile', () => {
    expect(petSetInBefore.canSmile).toBe(true)
  })
}

# __tests__/famous_animals.test.js
import { cutenessTests } from './cuteness'

describe('Famous animals', () => {
  let petSetInBefore;

  describe('Octocat', () => {
    beforeEach(() => {
      petSetInBefore = new Octocat();
    })

    cutenessTests.bind(this)()
  })
})

这里重要的是我试图共享多个test定义而不仅仅是一个，否则我可以将 petSetInBefore 传递给共享函数。

编辑：我的每个测试和嵌套描述都可能改变我的测试环境和对象，因此 beforeEach 用于恢复正确的测试环境。 这是一个更好的例子

class Octocat {
  get strokeFor(time) {
    this.strokeTime = this.strokeTime + time
    if (this.strokeTime <= 10) {
      this.mood = 'happy'
    } else {
      this.mood = 'bored'
    }
  }
}

class Doge {
  get strokeFor(time) {
    this.strokeTime = this.strokeTime + time
    if (this.strokeTime <= 5) {
      this.mood = 'happy'
    } else {
      this.mood = 'bored'
    }
  }
}

const cutenessTests = function() {
  describe('when stroked for a short while', () => {
    beforeEach(() => {
      petSetInBefore.strokeFor(1);
    })

    test('it is happy', () => { expect(petSetInBefore.mood).to(eq('happy')) }

    describe('when stroked too much', () => {
      beforeEach(() => {
        petSetInBefore.stroke(1000);
      })

      test('it gets bored', () => { expect(petSetInBefore.mood).to(eq('bored')) }
    })

    describe('when stroked a little longer', () => {
      beforeEach(() => {
        petSetInBefore.strokeFor(4);
      })

      test('it is still happy', () => { expect(petSetInBefore.mood).to(eq('happy')) }
    })
  })
}

EDIT2：这里是一个repl.it基于鬲的答案

EDIT3：在可重用测试之前或期间可以更改对象

describe('Famous animals', () => {
  let petSetInBefore;

  describe('Octocat', () => {
    beforeEach(() => {
      petSetInBefore = new Octocat();
    })

    describe('when it is not well rested', () => { 
      beforeEach(() => { petSetInBefore.wellRested() } // Extra object preparation / context before calling reusable examples
      cutenessTests()
    }),
    describe('when it is not well rested', () => { 
      // Calling reusable examples without extra context
      cutenessTests()
    })
  })
})

Answer 1

您可以简单地将共享测试移动到执行it()调用的函数中。

class Octocat {
  get length() {
    return 3;
  }

  get canSmile() {
    return true;
  }
}

class GrumpyCat {
  get length() {
    return 1;
  }

  get canSmile() {
    return false;
  }
}

const behavesLikeAPet = (pet) => {
  it('is small', () => expect(pet.length).toBeLessThan(5));
  it('can smile', () => expect(pet.canSmile).toEqual(true));
};

describe('Famous animals', () => {
  describe('Octocat', () => {
    behavesLikeAPet(new Octocat());
  });

  describe('GrumpyCat', () => {
    behavesLikeAPet(new GrumpyCat());
  });
});

您将获得每个 it 测试的详细输出：

Famous animals
  Octocat
    ✓ is small (2ms)
    ✓ can smile (1ms)
  GrumpyCat
    ✓ is small
    ✕ can smile (2ms)

Answer 2

如果你还想要beforeEach ，

出于某些原因......如果您在全局范围内声明变量，它会起作用

let petSetInBefore; // here it works
describe('Famous animals', () => {
  //let petSetInBefore; // here it's undefined

  describe('Octocat', ()  => {
    //let petSetInBefore; // undefined too

    beforeAll(() => {
      petSetInBefore = new Octocat();
    })

    cutenessTests() // .bind(this) results the same
  });

  describe('Doge', () => {
    beforeEach(() => {
      petSetInBefore = new Doge();
    })

    cutenessTests.bind(this)()
  });
})

https://repl.it/@gui3/jestSharedTests

似乎共享函数中的测试不能共享beforeEach 中的变量，否则......

Answer 3

Jest 有describe.each(table) ，我没有看到它被大量使用，但它对于重用具有共同/相同结果的测试非常有帮助。

如果对两个测试对象的期望相同，您可以这样做：

const aCutePet = pet => {
  it("should be small", () => {
    expect(pet.size).toBeLessThan(10);
  });

  it(`should be able to smile`, () => {
    expect(pet).toHaveProperty('can_smile', true)
  });
}

describe.each([
  [new Doge],
  [new Octocat]
])("The %O", aCutePet);

输出：

  The Doge { size: 3, can_smile: true }
    ✓ should be small (1ms)
    ✓ should be able to smile (1ms)
  The Octocat { size: 5, can_smile: true }
    ✓ should be small
    ✓ should be able to smile (1ms)