Update the test case for cancel behavior

Tests/Tests/SDWebImageManagerTests.m

@@ -62,13 +62,14 @@
 }
 
 - (void)test06CancellAll {
-    XCTestExpectation *expectation = [self expectationWithDescription:@"Cancel"];
+    XCTestExpectation *expectation = [self expectationWithDescription:@"Cancel should callback with error"];
     
     // need a bigger image here, that is why we don't use kTestJPEGURL
     // if the image is too small, it will get downloaded before we can cancel :)
     NSURL *url = [NSURL URLWithString:@"https://raw.githubusercontent.com/liyong03/YLGIFImage/master/YLGIFImageDemo/YLGIFImageDemo/joy.gif"];
     [[SDWebImageManager sharedManager] loadImageWithURL:url options:0 progress:nil completed:^(UIImage * _Nullable image, NSData * _Nullable data, NSError * _Nullable error, SDImageCacheType cacheType, BOOL finished, NSURL * _Nullable imageURL) {
-        XCTFail(@"Should not get here");
+        expect(error).notTo.beNil();
+        expect(error.code).equal(SDWebImageErrorCancelled);
     }];
     
     [[SDWebImageManager sharedManager] cancelAll];