Add a flush method to the FakeAsync zone spec (#755)

The `flush` method advances time until all non-periodic timers
are cleared from the queue. It has a configurable limit (default 20)
of tasks that will be run before it gives up and throws an error,
in order to avoid infinite loops when polling timeouts are present.

Closes #735

lib/zone-spec/fake-async-test.ts

@@ -13,6 +13,7 @@
     func: Function;
     args: any[];
     delay: number;
+    isPeriodic: boolean;
   }
 
   class Scheduler {
@@ -26,13 +27,21 @@
 
     constructor() {}
 
-    scheduleFunction(cb: Function, delay: number, args: any[] = [], id: number = -1): number {
+    scheduleFunction(
+        cb: Function, delay: number, args: any[] = [], isPeriodic: boolean = false,
+        id: number = -1): number {
       let currentId: number = id < 0 ? this.nextId++ : id;
       let endTime = this._currentTime + delay;
 
       // Insert so that scheduler queue remains sorted by end time.
-      let newEntry:
-          ScheduledFunction = {endTime: endTime, id: currentId, func: cb, args: args, delay: delay};
+      let newEntry: ScheduledFunction = {
+        endTime: endTime,
+        id: currentId,
+        func: cb,
+        args: args,
+        delay: delay,
+        isPeriodic: isPeriodic
+      };
       let i = 0;
       for (; i < this._schedulerQueue.length; i++) {
         let currentEntry = this._schedulerQueue[i];
@@ -73,6 +82,31 @@
       }
       this._currentTime = finalTime;
     }
+
+    flush(limit: number = 20): number {
+      const startTime = this._currentTime;
+      let count = 0;
+      while (this._schedulerQueue.length > 0) {
+        count++;
+        if (count > limit) {
+          throw new Error(
+              'flush failed after reaching the limit of ' + limit +
+              ' tasks. Does your code use a polling timeout?');
+        }
+        // If the only remaining tasks are periodic, finish flushing.
+        if (!(this._schedulerQueue.filter(task => !task.isPeriodic).length)) {
+          break;
+        }
+        let current = this._schedulerQueue.shift();
+        this._currentTime = current.endTime;
+        let retval = current.func.apply(global, current.args);
+        if (!retval) {
+          // Uncaught exception in the current scheduled function. Stop processing the queue.
+          break;
+        }
+      }
+      return this._currentTime - startTime;
+    }
   }
 
   class FakeAsyncTestZoneSpec implements ZoneSpec {
@@ -134,7 +168,7 @@
       return () => {
         // Requeue the timer callback if it's not been canceled.
         if (this.pendingPeriodicTimers.indexOf(id) !== -1) {
-          this._scheduler.scheduleFunction(fn, interval, args, id);
+          this._scheduler.scheduleFunction(fn, interval, args, true, id);
         }
       };
     }
@@ -168,7 +202,7 @@
       completers.onSuccess = this._requeuePeriodicTimer(cb, interval, args, id);
 
       // Queue the callback and dequeue the periodic timer only on error.
-      this._scheduler.scheduleFunction(cb, interval, args);
+      this._scheduler.scheduleFunction(cb, interval, args, true);
       this.pendingPeriodicTimers.push(id);
       return id;
     }
@@ -209,6 +243,16 @@
       flushErrors();
     }
 
+    flush(): number {
+      FakeAsyncTestZoneSpec.assertInZone();
+      this.flushMicrotasks();
+      let elapsed = this._scheduler.flush();
+      if (this._lastError !== null) {
+        this._resetLastErrorAndThrow();
+      }
+      return elapsed;
+    }
+
     // ZoneSpec implementation below.
 
     name: string;

test/zone-spec/fake-async-test.spec.ts

@@ -353,6 +353,148 @@ describe('FakeAsyncTestZoneSpec', () => {
     expect(testZoneSpec.pendingTimers.length).toBe(0);
   });
 
+  describe('flushing all tasks', () => {
+    it('should flush all pending timers', () => {
+      fakeAsyncTestZone.run(() => {
+        let x = false;
+        let y = false;
+        let z = false;
+
+        setTimeout(() => {
+          x = true;
+        }, 10);
+        setTimeout(() => {
+          y = true;
+        }, 100);
+        setTimeout(() => {
+          z = true;
+        }, 70);
+
+        let elapsed = testZoneSpec.flush();
+
+        expect(elapsed).toEqual(100);
+        expect(x).toBe(true);
+        expect(y).toBe(true);
+        expect(z).toBe(true);
+      });
+    });
+
+    it('should flush nested timers', () => {
+      fakeAsyncTestZone.run(() => {
+        let x = true;
+        let y = true;
+        setTimeout(() => {
+          x = true;
+          setTimeout(() => {
+            y = true;
+          }, 100);
+        }, 200);
+
+        let elapsed = testZoneSpec.flush();
+
+        expect(elapsed).toEqual(300);
+        expect(x).toBe(true);
+        expect(y).toBe(true);
+      });
+    });
+
+    it('should advance intervals', () => {
+      fakeAsyncTestZone.run(() => {
+        let x = false;
+        let y = false;
+        let z = 0;
+
+        setTimeout(() => {
+          x = true;
+        }, 50);
+        setTimeout(() => {
+          y = true;
+        }, 141);
+        setInterval(() => {
+          z++;
+        }, 10);
+
+        let elapsed = testZoneSpec.flush();
+
+        expect(elapsed).toEqual(141);
+        expect(x).toBe(true);
+        expect(y).toBe(true);
+        expect(z).toEqual(14);
+      });
+    });
+
+    it('should not wait for intervals', () => {
+      fakeAsyncTestZone.run(() => {
+        let z = 0;
+
+        setInterval(() => {
+          z++;
+        }, 10);
+
+        let elapsed = testZoneSpec.flush();
+
+        expect(elapsed).toEqual(0);
+        expect(z).toEqual(0);
+      });
+    });
+
+
+    it('should process micro-tasks created in timers before next timers', () => {
+      fakeAsyncTestZone.run(() => {
+        let log: string[] = [];
+
+        Promise.resolve(null).then((_) => log.push('microtask'));
+
+        setTimeout(() => {
+          log.push('timer');
+          Promise.resolve(null).then((_) => log.push('t microtask'));
+        }, 20);
+
+        let id = setInterval(() => {
+          log.push('periodic timer');
+          Promise.resolve(null).then((_) => log.push('pt microtask'));
+        }, 10);
+
+        testZoneSpec.flush();
+        expect(log).toEqual(
+            ['microtask', 'periodic timer', 'pt microtask', 'timer', 't microtask']);
+      });
+    });
+
+    it('should throw the exception from tick for error thrown in timer callback', () => {
+      fakeAsyncTestZone.run(() => {
+        setTimeout(() => {
+          throw new Error('timer');
+        }, 10);
+        expect(() => {
+          testZoneSpec.flush();
+        }).toThrowError('timer');
+      });
+      // There should be no pending timers after the error in timer callback.
+      expect(testZoneSpec.pendingTimers.length).toBe(0);
+    });
+
+    it('should do something reasonable with polling timeouts', () => {
+      expect(() => {
+        fakeAsyncTestZone.run(() => {
+          let z = 0;
+
+          let poll = () => {
+            setTimeout(() => {
+              z++;
+              poll();
+            }, 10);
+          };
+
+          poll();
+          testZoneSpec.flush();
+        });
+      })
+          .toThrowError(
+              'flush failed after reaching the limit of 20 tasks. Does your code use a polling timeout?');
+    });
+  });
+
   describe('outside of FakeAsync Zone', () => {
     it('calling flushMicrotasks should throw exception', () => {
       expect(() => {