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diff --git a/Firestore/Example/Tests/Util/FSTDispatchQueueTests.mm b/Firestore/Example/Tests/Util/FSTDispatchQueueTests.mm
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+/*
+ * Copyright 2018 Google
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#import "Firestore/Source/Util/FSTDispatchQueue.h"
+
+#import <XCTest/XCTest.h>
+
+#import "Firestore/Example/Tests/Util/XCTestCase+Await.h"
+
+// In these generic tests the specific TimerIDs don't matter.
+static const FSTTimerID timerID1 = FSTTimerIDListenStreamConnection;
+static const FSTTimerID timerID2 = FSTTimerIDListenStreamIdle;
+static const FSTTimerID timerID3 = FSTTimerIDWriteStreamConnection;
+
+@interface FSTDispatchQueueTests : XCTestCase
+@end
+
+@implementation FSTDispatchQueueTests {
+  FSTDispatchQueue *_queue;
+  NSMutableArray *_completedSteps;
+  NSArray *_expectedSteps;
+  XCTestExpectation *_expectation;
+}
+
+- (void)setUp {
+  [super setUp];
+  dispatch_queue_t dispatch_queue =
+      dispatch_queue_create("FSTDispatchQueueTests", DISPATCH_QUEUE_SERIAL);
+  _queue = [[FSTDispatchQueue alloc] initWithQueue:dispatch_queue];
+  _completedSteps = [NSMutableArray array];
+  _expectedSteps = nil;
+}
+
+/**
+ * Helper to return a block that adds @(n) to _completedSteps when run and fulfils _expectation if
+ * the _completedSteps match the _expectedSteps.
+ */
+- (void (^)())blockForStep:(int)n {
+  return ^void() {
+    [self->_completedSteps addObject:@(n)];
+    if (self->_expectedSteps && self->_completedSteps.count >= self->_expectedSteps.count) {
+      XCTAssertEqualObjects(self->_completedSteps, self->_expectedSteps);
+      [self->_expectation fulfill];
+    }
+  };
+}
+
+- (void)testCanScheduleCallbacksInTheFuture {
+  _expectation = [self expectationWithDescription:@"Expected steps"];
+  _expectedSteps = @[ @1, @2, @3, @4 ];
+  [_queue dispatchAsync:[self blockForStep:1]];
+  [_queue dispatchAfterDelay:0.005 timerID:timerID1 block:[self blockForStep:4]];
+  [_queue dispatchAfterDelay:0.001 timerID:timerID2 block:[self blockForStep:3]];
+  [_queue dispatchAsync:[self blockForStep:2]];
+
+  [self awaitExpectations];
+}
+
+- (void)testCanCancelDelayedCallbacks {
+  _expectation = [self expectationWithDescription:@"Expected steps"];
+  _expectedSteps = @[ @1, @3 ];
+  // Queue everything from the queue to ensure nothing completes before we cancel.
+  [_queue dispatchAsync:^{
+    [_queue dispatchAsyncAllowingSameQueue:[self blockForStep:1]];
+    FSTDelayedCallback *step2Timer =
+        [_queue dispatchAfterDelay:.001 timerID:timerID1 block:[self blockForStep:2]];
+    [_queue dispatchAfterDelay:.005 timerID:timerID2 block:[self blockForStep:3]];
+
+    XCTAssertTrue([_queue containsDelayedCallbackWithTimerID:timerID1]);
+    [step2Timer cancel];
+    XCTAssertFalse([_queue containsDelayedCallbackWithTimerID:timerID1]);
+  }];
+
+  [self awaitExpectations];
+}
+
+- (void)testCanManuallyDrainAllDelayedCallbacksForTesting {
+  [_queue dispatchAsync:[self blockForStep:1]];
+  [_queue dispatchAfterDelay:20 timerID:timerID1 block:[self blockForStep:4]];
+  [_queue dispatchAfterDelay:10 timerID:timerID2 block:[self blockForStep:3]];
+  [_queue dispatchAsync:[self blockForStep:2]];
+
+  [_queue runDelayedCallbacksUntil:FSTTimerIDAll];
+  XCTAssertEqualObjects(_completedSteps, (@[ @1, @2, @3, @4 ]));
+}
+
+- (void)testCanManuallyDrainSpecificDelayedCallbacksForTesting {
+  [_queue dispatchAsync:[self blockForStep:1]];
+  [_queue dispatchAfterDelay:20 timerID:timerID1 block:[self blockForStep:5]];
+  [_queue dispatchAfterDelay:10 timerID:timerID2 block:[self blockForStep:3]];
+  [_queue dispatchAfterDelay:15 timerID:timerID3 block:[self blockForStep:4]];
+  [_queue dispatchAsync:[self blockForStep:2]];
+
+  [_queue runDelayedCallbacksUntil:timerID3];
+  XCTAssertEqualObjects(_completedSteps, (@[ @1, @2, @3, @4 ]));
+}
+
+@end