test(docs-infra): add missing unit tests for backoff example (#38896)

This commit adds the missing unit test for the backoff example.

PR Close #38896

aio/content/examples/practical-observable-usage/src/backoff.spec.ts

@@ -0,0 +1,70 @@
+import { interval } from 'rxjs';
+import { tap } from 'rxjs/operators';
+import { backoff } from './backoff';
+
+describe('backoff()', () => {
+  beforeEach(() => jasmine.clock().install());
+  afterEach(() => jasmine.clock().uninstall());
+
+  it('should retry in case of error', () => {
+    const mockConsole = {log: jasmine.createSpy('log')};
+    const source = interval(10).pipe(
+      tap(i => {
+        if (i > 0) {
+          throw new Error('Test error');
+        }
+      }),
+      backoff(3, 100),
+    );
+    source.subscribe({
+      next: v => mockConsole.log(`Emitted: ${v}`),
+      error: e => mockConsole.log(`Errored: ${e.message || e}`),
+      complete: () => mockConsole.log('Completed'),
+    });
+
+    // Initial try:
+    // Errors on second emission and schedules retrying (with delay).
+    jasmine.clock().tick(10);
+    expect(mockConsole.log.calls.allArgs()).toEqual([['Emitted: 0']]);
+
+    jasmine.clock().tick(10);
+    expect(mockConsole.log.calls.allArgs()).toEqual([['Emitted: 0']]);
+    mockConsole.log.calls.reset();
+
+    // First re-attempt after 100ms:
+    // Errors again on second emission and schedules retrying (with larger delay).
+    jasmine.clock().tick(100);
+    expect(mockConsole.log).not.toHaveBeenCalled();
+
+    jasmine.clock().tick(10);
+    expect(mockConsole.log.calls.allArgs()).toEqual([['Emitted: 0']]);
+
+    jasmine.clock().tick(10);
+    expect(mockConsole.log.calls.allArgs()).toEqual([['Emitted: 0']]);
+    mockConsole.log.calls.reset();
+
+    // Second re-attempt after 400ms:
+    // Errors again on second emission and schedules retrying (with even larger delay).
+    jasmine.clock().tick(400);
+    expect(mockConsole.log).not.toHaveBeenCalled();
+
+    jasmine.clock().tick(10);
+    expect(mockConsole.log.calls.allArgs()).toEqual([['Emitted: 0']]);
+
+    jasmine.clock().tick(10);
+    expect(mockConsole.log.calls.allArgs()).toEqual([['Emitted: 0']]);
+    mockConsole.log.calls.reset();
+
+    // Third re-attempt after 900ms:
+    // Errors again on second emission and gives up (no retrying).
+    jasmine.clock().tick(900);
+    expect(mockConsole.log).not.toHaveBeenCalled();
+
+    jasmine.clock().tick(10);
+    expect(mockConsole.log.calls.allArgs()).toEqual([['Emitted: 0']]);
+    mockConsole.log.calls.reset();
+
+    jasmine.clock().tick(10);
+    expect(mockConsole.log.calls.allArgs()).toEqual([['Errored: Test error']]);
+  });
+});

aio/content/examples/practical-observable-usage/src/backoff.ts

@@ -1,9 +1,10 @@
-// TODO: Add unit tests for this file.
+// #docplaster
+// #docregion
 import { of, pipe, range, throwError, timer, zip } from 'rxjs';
 import { ajax } from 'rxjs/ajax';
 import { map, mergeMap, retryWhen } from 'rxjs/operators';
 
-function backoff(maxTries, delay) {
+export function backoff(maxTries, delay) {
   return pipe(
     retryWhen(attempts =>
       zip(range(1, maxTries + 1), attempts).pipe(
@@ -15,10 +16,17 @@ function backoff(maxTries, delay) {
   );
 }
 
+// #enddocregion
+/*
+  This function declaration is necessary to ensure that it does not get called
+  when running the unit tests. It will not get rendered into the docs.
+  The indentation needs to start in the leftmost level position as well because of how
+  the docplaster combines the different regions together.
+*/
+function docRegionAjaxCall() {
+// #docregion
 ajax('/api/endpoint')
   .pipe(backoff(3, 250))
-  .subscribe(data => handleData(data));
-
-function handleData(data) {
-  // ...
+  .subscribe(function handleData(data) { /* ... */ });
+// #enddocregion
 }