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firstValueFrom-spec.ts
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firstValueFrom-spec.ts
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import { interval, firstValueFrom, EMPTY, EmptyError, throwError, of, Observable } from 'rxjs';
import { expect } from 'chai';
import { finalize } from 'rxjs/operators';
describe('firstValueFrom', () => {
it('should emit the first value as a promise', async () => {
let finalized = false;
const source = interval(10).pipe(finalize(() => (finalized = true)));
const result = await firstValueFrom(source);
expect(result).to.equal(0);
expect(finalized).to.be.true;
});
it('should support a default value', async () => {
const source = EMPTY;
const result = await firstValueFrom(source, { defaultValue: 0 });
expect(result).to.equal(0);
});
it('should support an undefined config', async () => {
const source = EMPTY;
let error: any = null;
try {
await firstValueFrom(source, undefined as any);
} catch (err) {
error = err;
}
expect(error).to.be.an.instanceOf(EmptyError);
});
it('should error for empty observables', async () => {
const source = EMPTY;
let error: any = null;
try {
await firstValueFrom(source);
} catch (err) {
error = err;
}
expect(error).to.be.an.instanceOf(EmptyError);
});
it('should error for errored observables', async () => {
const source = throwError(new Error('blorp!'));
let error: any = null;
try {
await firstValueFrom(source);
} catch (err) {
error = err;
}
expect(error).to.be.an.instanceOf(Error);
expect(error.message).to.equal('blorp!');
});
it('should work with a synchronous observable', async () => {
let finalized = false;
const source = of('apples', 'bananas').pipe(finalize(() => (finalized = true)));
const result = await firstValueFrom(source);
expect(result).to.equal('apples');
expect(finalized).to.be.true;
});
it('should stop listening to a synchronous observable when resolved', async () => {
const sideEffects: number[] = [];
const synchronousObservable = new Observable<number>(subscriber => {
// This will check to see if the subscriber was closed on each loop
// when the unsubscribe hits (from the `take`), it should be closed
for (let i = 0; !subscriber.closed && i < 10; i++) {
sideEffects.push(i);
subscriber.next(i);
}
});
const result = await firstValueFrom(synchronousObservable);
expect(sideEffects).to.deep.equal([0]);
});
});