Add test for decrement

Author: tejasd

firebase-perf/src/test/java/com/google/firebase/perf/session/gauges/GaugeManagerTest.java

@@ -371,6 +371,36 @@ public void testGaugeCounterStartsAJobToConsumeTheGeneratedMetrics() throws Inte
     assertThat(recordedGaugeMetric.getSessionId()).isEqualTo(testSessionId(1));
   }
 
+  @Test
+  public void testGaugeCounterIsDecrementedWhenLogged() throws InterruptedException {
+    int priorGaugeCounter = GaugeCounter.count();
+
+    PerfSession fakeSession = createTestSession(1);
+    testGaugeManager.setApplicationProcessState(ApplicationProcessState.FOREGROUND);
+    testGaugeManager.startCollectingGauges(fakeSession);
+    GaugeCounter.setGaugeManager(testGaugeManager);
+
+    // There's no job to log the gauges.
+    assertThat(fakeScheduledExecutorService.isEmpty()).isTrue();
+
+    // Generate metrics that don't exceed the GaugeCounter.MAX_COUNT.
+    generateMetricsAndIncrementCounter(20);
+
+    // There's still no job to log the gauges.
+    assertThat(fakeScheduledExecutorService.isEmpty()).isTrue();
+
+    generateMetricsAndIncrementCounter(10);
+
+    assertThat(fakeScheduledExecutorService.isEmpty()).isFalse();
+    assertThat(fakeScheduledExecutorService.getDelayToNextTask(TimeUnit.MILLISECONDS))
+        .isEqualTo(TIME_TO_WAIT_BEFORE_FLUSHING_GAUGES_QUEUE_MS);
+
+    assertThat(GaugeCounter.count()).isEqualTo(priorGaugeCounter + 30);
+    fakeScheduledExecutorService.simulateSleepExecutingAtMostOneTask();
+
+    assertThat(GaugeCounter.count()).isEqualTo(priorGaugeCounter);
+  }
+
   @Test
   public void testUpdateAppStateHandlesMultipleAppStates() {
     PerfSession fakeSession = createTestSession(1);