Thread safe creation and canceling of download tasks

fixes #364

AsyncDisplayKitTests/ASBasicImageDownloaderContextTests.m

@@ -0,0 +1,72 @@
+/* Copyright (c) 2014-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+
+#import <AsyncDisplayKit/ASBasicImageDownloaderInternal.h>
+#import <AsyncDisplayKit/ASBasicImageDownloader.h>
+
+#import <OCMock/OCMock.h>
+
+#import <XCTest/XCTest.h>
+
+
+@interface ASBasicImageDownloaderContextTests : XCTestCase
+
+@end
+
+@implementation ASBasicImageDownloaderContextTests
+
+- (NSURL *)randomURL
+{
+  // random URL for each test, doesn't matter that this is not really a URL
+  return [NSURL URLWithString:[NSUUID UUID].UUIDString];
+}
+
+- (void)testContextCreation
+{
+  NSURL *url = [self randomURL];
+  ASBasicImageDownloaderContext *c1 = [ASBasicImageDownloaderContext contextForURL:url];
+  ASBasicImageDownloaderContext *c2 = [ASBasicImageDownloaderContext contextForURL:url];
+  XCTAssert(c1 == c2, @"Context objects are not the same");
+}
+
+- (void)testContextInvalidation
+{
+  NSURL *url = [self randomURL];
+  ASBasicImageDownloaderContext *context = [ASBasicImageDownloaderContext contextForURL:url];
+  [context cancel];
+  XCTAssert([context isCancelled], @"Context should be cancelled");
+}
+
+- (void)testAsyncContextInvalidation
+{
+  NSURL *url = [self randomURL];
+  ASBasicImageDownloaderContext *context = [ASBasicImageDownloaderContext contextForURL:url];
+  XCTestExpectation *expectation = [self expectationWithDescription:@"Context invalidation"];
+
+  dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
+    [expectation fulfill];
+    XCTAssert([context isCancelled], @"Context should be cancelled");
+  });
+
+  [context cancel];
+  [self waitForExpectationsWithTimeout:0.1 handler:nil];
+}
+
+- (void)testContextSessionCanceled
+{
+  NSURL *url = [self randomURL];
+  id task = [OCMockObject mockForClass:[NSURLSessionTask class]];
+  ASBasicImageDownloaderContext *context = [ASBasicImageDownloaderContext contextForURL:url];
+  context.sessionTask = task;
+
+  [[task expect] cancel];
+
+  [context cancel];
+}
+
+@end