[英]rxjs how to expect an observable to throw error
In my TypeScript app I have a method that return an rxjs Observable which, in a certain case, can return throwError :在我的 TypeScript 应用程序中,我有一个返回 rxjs Observable 的方法,在某些情况下,它可以返回throwError :
import { throwError } from 'rxjs';
// ...
getSomeData(inputValue): Observable<string> {
if (!inputValue) {
return throwError('Missing inputValue!');
}
// ...
}
how can I write a test to cover this specific case?我如何编写测试来涵盖这个特定案例?
You can test it using RxJS Marble diagram tests.您可以使用 RxJS Marble 图表测试来测试它。 Here's how:就是这样:
const getSomeData = (inputValue: string): Observable<string> => {
if (!inputValue) {
return throwError('Missing inputValue!');
}
// e.g.
return of(inputValue);
};
describe('Error test', () => {
let scheduler: TestScheduler;
beforeEach(() => {
scheduler = new TestScheduler((actual, expected) => {
expect(actual).toEqual(expected);
});
});
it('should throw an error if an invalid value has been sent', () => {
scheduler.run(({ expectObservable }) => {
const expectedMarbles = '#'; // # indicates an error terminal event
const result$ = getSomeData(''); // an empty string is falsy
expectObservable(result$).toBe(expectedMarbles, null, 'Missing inputValue!');
});
});
it('should emit an inputValue and immediately complete', () => {
scheduler.run(({ expectObservable }) => {
const expectedMarbles = '(a|)';
const result$ = getSomeData('Some valid string');
expectObservable(result$).toBe(expectedMarbles, { a: 'Some valid string' });
});
});
});
For more info on how to write these tests, please take a look at this link .有关如何编写这些测试的更多信息,请查看此链接。
I imagine your full case resembles something like this我想你的完整案例类似于这样的东西
// first there is something that emits an Observable
export function doSomethingThatReturnsAnObservable() {
return createSomehowFirstObservable()
.pipe(
// then you take the data emitted by the first Observable
// and try to do something else which will emit another Observable
// therefore you have to use an operator like concatMap or switchMap
// this something else is where your error condition can occur
// and it is where we use your getSomeData() function
switchMap(inputValue => getSomeData(inputValue))
);
}
}
// eventually, somewhere else, you subscribe
doSomethingThatReturnsAnObservable()
.subscribe(
data => doStuff(data),
error => handleError(error),
() => doSomethingWhenCompleted()
)
A test for the error condition could look something like this错误条件的测试可能看起来像这样
it('test error condition'), done => {
// create the context so that the call to the code generates an error condition
.....
doSomethingThatReturnsAnObservable()
.subscribe(
null, // you are not interested in the case something is emitted
error => {
expect(error).to.equal(....);
done();
},
() => {
// this code should not be executed since an error condition is expected
done('Error, the Observable is expected to error and not complete');
}
)
})
In addition to lagoman's answer.除了拉戈曼的回答。 You could simplify the way to get the testScheduler.您可以简化获取 testScheduler 的方法。
describe('Error test', () => {
it('should throw an error if an invalid value has been sent', () => {
getTestScheduler().run(({ expectObservable }) => { // getTestScheduler from jasmine-marbles package
const expectedMarbles = '#'; // # indicates an error terminal event
const result$ = getSomeData(''); // an empty string is falsy
expectObservable(result$).toBe(expectedMarbles, null, 'Missing inputValue!');
});
});
it('should emit an inputValue and immediately complete', () => {
getTestScheduler().run(({ expectObservable }) => {
const expectedMarbles = '(a|)';
const result$ = getSomeData('Some valid string');
expectObservable(result$).toBe(expectedMarbles, { a: 'Some valid string' });
});
});
});
Another way is to check that the operator thows an error is to pipe it like below.另一种方法是检查操作员是否显示错误,如下所示对其进行管道传输。 I assume that you are using Chai.我假设您正在使用 Chai。
import { catchError } from 'rxjs/operators';
it('must throw an error', done => {
getSomeData().pipe(catchError((e) => [e])).subscribe(e => {
expect(e).to.be.an.instanceof(Error);
done();
})
})
Source How to test an RxJS operation that throws an error Source 如何测试抛出错误的 RxJS 操作
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