Jest spyOn仅在第二次调用和第三次调用时模拟实现
Jest spyOn仅在第二次调用和第三次调用时模拟实现
提问于 2020-04-27 09:40:26
我有一个函数，我只想在第二次调用和第三次调用时模拟它，但在第一次调用时使用默认实现。我看过Jest文档，有一个函数mockImplementationOnce可以用来模拟单个调用的实现。
有没有一个我可以使用的函数，让它对第一次调用使用默认实现，而只模拟第二次和第三次调用？
let functionCalls = 0;
const database = {
fetchValues() {
fetchValues();
fetchValues();
},
};
jest.spyOn(database, 'fetchValues')
.useDefaultImplementation() // <-- is there such a function?
.mockImplementationOnce(() => 42)
.mockImplementationOnce(() => 42)回答 1
Stack Overflow用户
发布于 2020-04-27 11:11:21
您可以使用mockImplementation方法模拟默认实现。请参阅mock-implementations
例如。
const database = {
fetchValues() {
return 'real data';
},
};
describe('61450440', () => {
afterEach(() => {
jest.restoreAllMocks();
});
it('should pass', () => {
jest
.spyOn(database, 'fetchValues')
.mockImplementation(() => 'default')
.mockImplementationOnce(() => 'first call')
.mockImplementationOnce(() => 'second call');
console.log(
[database.fetchValues(), database.fetchValues(), database.fetchValues(), database.fetchValues()].join(','),
);
});
it('should pass too', () => {
jest
.spyOn(database, 'fetchValues')
.mockImplementation(() => 'real data')
.mockImplementationOnce(() => 'real data')
.mockImplementationOnce(() => 'first call')
.mockImplementationOnce(() => 'second call');
console.log(
[database.fetchValues(), database.fetchValues(), database.fetchValues(), database.fetchValues()].join(','),
);
});
it('should pass 3', () => {
const fetchValuesSpy = jest.spyOn(database, 'fetchValues');
console.log('call original fetchValues:', database.fetchValues());
fetchValuesSpy.mockImplementationOnce(() => 'first call').mockImplementationOnce(() => 'second call');
console.log('call mocked fetchValues:', database.fetchValues(), database.fetchValues());
console.log('call original fetchValues again:', database.fetchValues());
});
});测试结果：
PASS stackoverflow/61450440/index.test.ts (13.748s)
61450440
✓ should pass (20ms)
✓ should pass too (1ms)
✓ should pass 3 (12ms)
console.log stackoverflow/61450440/index.test.ts:15
first call,second call,default,default
console.log stackoverflow/61450440/index.test.ts:27
real data,first call,second call,real data
console.log stackoverflow/61450440/index.test.ts:34
call original fetchValues: real data
console.log stackoverflow/61450440/index.test.ts:36
call mocked fetchValues: first call second call
console.log stackoverflow/61450440/index.test.ts:37
call original fetchValues again: real data
Test Suites: 1 passed, 1 total
Tests: 3 passed, 3 total
Snapshots: 0 total
Time: 15.761s页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/61450440
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