Add test case for coder priority in SDAnimatedImage

Tests/Tests/SDAnimatedImageTest.m

@@ -13,6 +13,41 @@
 
 static const NSUInteger kTestGIFFrameCount = 5; // local TestImage.gif loop count
 
+// Check whether the coder is called
+@interface SDImageAPNGTestCoder : SDImageAPNGCoder
+
+@property (nonatomic, class, assign) BOOL isCalled;
+
+@end
+
+@implementation SDImageAPNGTestCoder
+
+static BOOL _isCalled;
+
++ (BOOL)isCalled {
+    return _isCalled;
+}
+
++ (void)setIsCalled:(BOOL)isCalled {
+    _isCalled = isCalled;
+}
+
++ (instancetype)sharedCoder {
+    static SDImageAPNGTestCoder *coder;
+    static dispatch_once_t onceToken;
+    dispatch_once(&onceToken, ^{
+        coder = [[SDImageAPNGTestCoder alloc] init];
+    });
+    return coder;
+}
+
+- (instancetype)initWithAnimatedImageData:(NSData *)data options:(SDImageCoderOptions *)options {
+    SDImageAPNGTestCoder.isCalled = YES;
+    return [super initWithAnimatedImageData:data options:options];
+}
+
+@end
+
 // Internal header
 @interface SDAnimatedImageView ()
 
@@ -561,6 +596,12 @@ static const NSUInteger kTestGIFFrameCount = 5; // local TestImage.gif loop coun
     [self waitForExpectationsWithCommonTimeout];
 }
 
+- (void)test30AnimatedImageCoderPriority {
+    [SDImageCodersManager.sharedManager addCoder:SDImageAPNGTestCoder.sharedCoder];
+    [SDAnimatedImage imageWithData:[self testAPNGPData]];
+    expect(SDImageAPNGTestCoder.isCalled).equal(YES);
+}
+
 #pragma mark - Helper
 - (UIWindow *)window {
     if (!_window) {