我需要测试一个函数(example()),它使用另一个函数(validateDataset).因为我只想测试example()函数,所以我模拟了validateDataset().
当然,每个测试都需要模拟函数的不同结果.但是如何为模拟函数设置不同的promise结果？在我下面显示的尝试中,模拟函数始终返回相同的值.
所以在这个例子中,我无法测试抛出的错误.
functions.js
import { validateDataset } from './helper/validation'
export async function example (id) {
const { docElement } = await validateDataset(id)
if (!docElement) throw Error('Missing content')
return docElement
}
functions.test.js
import { example } from './functions'
jest.mock('./helper/validation',() => ({
validateDataset: jest.fn(() => Promise.resolve({
docMain: {},docElement: {
data: 'result'
}
}))
}))
describe('example()',() => {
test('should return object',async () => {
const result = await example('123')
expect(result.data).toBe('result')
})
test('should throw error',async () => {
const result = await example('123')
// How to get different result (`null`) in this test
// How to test for the thrown error?
})
})
解决方法
Jest模拟的好处在于,你可以模拟整个模块,并且通过要求它的默认或命名导出,你仍然可以得到一个模拟,你可以实现和重新实现,无论你喜欢什么.
我发布了一个测试的示例实现,期望validateDataset调用失败.为简洁起见,我还留了一些评论.
import { example } from './example';
import { validateDataset } from './helper/validation';
// Declare export of './helper/validation' as a Mock Function.
// It marks all named exports inside as Mock Functions too.
jest.mock('./helper/validation');
test('example() should return object',async () => {
// Because `validateDataset` is already mocked,we can provide
// an implementation. For this test we'd like it to be original one.
validateDataset.mockImplementation(() => {
// `jest.requireActual` calls unmocked module
return jest.requireActual('./helper/validation').validateDataset();
});
const result = await example('123');
expect(result.data).toBe('result');
});
test('example() should throw error',async () => {
// Worth to make sure our async assertions are actually made
expect.assertions(1);
// We can adjust the implementation of `validateDataset` however we like,// because it's a Mock Function. So we return a null `docElement`
validateDataset.mockImplementation(() => ({ docElement: null }));
try {
await example('123');
} catch (error) {
expect(error.message).toEqual('Missing content');
}
});
希望能把事情搞清楚.
