如何在 Jest 中的 beforeAll / beforeEach 和测试之间共享数据？

Question

我们使用 jest 来测试我们的 API，并且有相当复杂的场景。我们使用beforeAll 函数为每个测试设置通用帮助变量，有时设置租户分离，在其他情况下，我们使用beforeEach 函数为测试设置租户分离，并为测试设置一些默认配置租户，...

例如，测试可能像这样（如您所见，我们使用 TypeScript 来编写测试，以防万一）：

let apiClient: ApiClient;
let tenantId: string;

beforeAll(async () => {
    apiClient = await getClientWithCredentials();
});

beforeEach(async () => {
    tenantId = await createNewTestTenant();
});

describe('describing complex test scenario', () => {
    it('should have some initial state', async () => {
        await checkState(tenantId);
    });

    it('should have some state after performing op1', async () =>{
        await op1(tenantId);
        await checkStateAfterOp1(tenantId);
    });

    it('should have some state after performing op2', async () =>{
        await op2(tenantId);
        await checkStateAfterOp2(tenantId);
    });

    it('should have some state after performing op1 and op2', async () =>{
        await op1(tenantId);
        await op2(tenantId);
        await checkStateAfterOp1AndOp2(tenantId);
    });

    it('the order of op1 and op2 should not matter', async () =>{
        await op2(tenantId);
        await op1(tenantId);
        await checkStateAfterOp1AndOp2(tenantId);
    });    
});

describe('another similar complex scenario', () => {
    // ... you see where this is going
});

问题是，共享由beforeAll 和beforeEach 初始化的变量的最佳方式是什么？ - 如果使用--runInBand 选项执行上述测试，"... 在当前进程中连续运行所有测试..."

但是当并行执行时，它开始非常随机地失败，主要是指tenantId 未定义。鉴于这些测试是大约 200 个类似测试的一部分，因此全部通过。同时，它取决于机器。具有 8 核 / 16 线程的构建代理只有 50-60% 通过测试。我的四核 CPU 同事通过了约 80% 的测试，而对我来说，双核 CPU 有时只有 1-2 次测试失败，其他时候约 10 次。所以显然这取决于并行度。

我发现了 2 个 GitHub 问题，人们提到可以使用 this 共享上下文（不再起作用）或将所有内容封装在 describe 中：

• https://github.com/facebook/jest/issues/3553
• https://github.com/facebook/jest/issues/3673

所以我尝试了一个非常幼稚的方法：

describe('tests', () => {
    let apiClient: ApiClient;
    let tenantId: string;

    beforeAll(async () => {
        apiClient = await getClientWithCredentials();
    });

    beforeEach(async () => {
        tenantId = await createNewTestTenant();
    });

    describe('describing complex test scenario', () => {
        it('should have some initial state', async () => {
            await checkState(tenantId);
        });

        it('should have some state after performing op1', async () =>{
            await op1(tenantId);
            await checkStateAfterOp1(tenantId);
        });

        it('should have some state after performing op2', async () =>{
            await op2(tenantId);
            await checkStateAfterOp2(tenantId);
        });

        it('should have some state after performing op1 and op2', async () =>{
            await op1(tenantId);
            await op2(tenantId);
            await checkStateAfterOp1AndOp2(tenantId);
        });

        it('the order of op1 and op2 should not matter', async () =>{
            await op2(tenantId);
            await op1(tenantId);
            await checkStateAfterOp1AndOp2(tenantId);
        });    
    });

    describe('another similar complex scenario', () => {
        // ... you see where this is going
    });
});

但这似乎没有任何效果。 我真的很想并行运行测试，但我在文档中找不到任何相关内容。也许我不知道我应该寻找什么？

Answer 1

这对你有用吗？

describe('tests', () => {
    let apiClient: ApiClient;
    let tenantIds: {id: string, used: boolean}[];

    const findUnusedTenantId = () => {
      const tenant = tenantIds.find(a => !a.used);
      tenant.used = true; 
      return tenant.id
    }

    beforeAll(async () => {
        apiClient = await getClientWithCredentials();
    });

    beforeEach(async () => {
        const id = await createNewTestTenant();
        tenantIds.push({id, used: false})
    });

    describe('describing complex test scenario', () => {
        let tenantId: string
        it('should have some initial state', async () => {
            tenantId = fineUnusedTenantId();
            await checkState(tenantId);
        });

        it('should have some state after performing op1', async () =>{
            await op1(tenantId);
            await checkStateAfterOp1(tenantId);
        });

        // ...
    });
    describe('next scenario', () => {
        let tenantId: string
        it('first test', async () => {
            tenantId = fineUnusedTenantId();
            await checkState(tenantId);
        });

你可能想要一个 afterAll 挂钩来清理数据库