Added the test case `testEncodingGrayscaleImage` about grayscale

Tests/SDWebImageWebPCoderTests.m

@@ -292,6 +292,35 @@ const int64_t kAsyncTestTimeout = 5;
     expect(config.method).to.equal(4);
 }
 
+
+- (void)testEncodingGrayscaleImage {
+    NSURL *grayscaleImageURL = [[NSBundle bundleForClass:[self class]] URLForResource:@"TestImageGrayscale" withExtension:@"jpg"];
+    NSData *grayscaleImageData = [NSData dataWithContentsOfURL:grayscaleImageURL];
+    UIImage *grayscaleImage = [[UIImage alloc] initWithData:grayscaleImageData];
+    expect(grayscaleImage).notTo.beNil();
+    
+    NSData *webpData = [SDImageWebPCoder.sharedCoder encodedDataWithImage:grayscaleImage format:SDImageFormatWebP options:nil];
+    expect(webpData).notTo.beNil();
+    
+    UIImage *decodedImage = [UIImage sd_imageWithData:webpData];
+    expect(decodedImage).notTo.beNil();
+    
+    // Sample to verify that encoded WebP image's color is correct.
+    // The wrong case before bugfix is that each column color will repeats 3 times.
+    CGPoint point1 = CGPointMake(271, 764);
+    CGPoint point2 = CGPointMake(round(point1.x + decodedImage.size.width / 3), point1.y);
+    UIColor *color1 = [decodedImage sd_colorAtPoint:point1];
+    UIColor *color2 = [decodedImage sd_colorAtPoint:point2];
+    CGFloat r1, r2;
+    CGFloat g1, g2;
+    CGFloat b1, b2;
+    [color1 getRed:&r1 green:&g1 blue:&b1 alpha:nil];
+    [color2 getRed:&r2 green:&g2 blue:&b2 alpha:nil];
+    expect(255 * r1).notTo.equal(255 * r2);
+    expect(255 * g1).notTo.equal(255 * g2);
+    expect(255 * b1).notTo.equal(255 * b2);
+}
+
 @end
 
 @implementation SDWebImageWebPCoderTests (Helpers)

Tests/SDWebImageWebPCoderTests.xcodeproj/project.pbxproj

@@ -9,6 +9,7 @@
 /* Begin PBXBuildFile section */
 		0EF5B6264833B7BC20894578 /* Pods_SDWebImageWebPCoderTests.framework in Frameworks */ = {isa = PBXBuildFile; fileRef = 46F21AD7D1692EBAC4D0FF33 /* Pods_SDWebImageWebPCoderTests.framework */; };
 		3219F3B2228B0453003822A6 /* TestImageBlendAnimated.webp in Resources */ = {isa = PBXBuildFile; fileRef = 3219F3B1228B0453003822A6 /* TestImageBlendAnimated.webp */; };
+		325E268E25C82BE1000B807B /* TestImageGrayscale.jpg in Resources */ = {isa = PBXBuildFile; fileRef = 325E268D25C82BE1000B807B /* TestImageGrayscale.jpg */; };
 		808C918E213FD131004B0F7C /* SDWebImageWebPCoderTests.m in Sources */ = {isa = PBXBuildFile; fileRef = 808C918D213FD131004B0F7C /* SDWebImageWebPCoderTests.m */; };
 		808C919C213FD2B2004B0F7C /* TestImageStatic.webp in Resources */ = {isa = PBXBuildFile; fileRef = 808C919A213FD2B2004B0F7C /* TestImageStatic.webp */; };
 		808C919D213FD2B2004B0F7C /* TestImageAnimated.webp in Resources */ = {isa = PBXBuildFile; fileRef = 808C919B213FD2B2004B0F7C /* TestImageAnimated.webp */; };
@@ -17,6 +18,7 @@
 /* Begin PBXFileReference section */
 		28D8AA3D3015E075692FD3E3 /* Pods-SDWebImageWebPCoderTests.debug.xcconfig */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = text.xcconfig; name = "Pods-SDWebImageWebPCoderTests.debug.xcconfig"; path = "../Pods/Target Support Files/Pods-SDWebImageWebPCoderTests/Pods-SDWebImageWebPCoderTests.debug.xcconfig"; sourceTree = "<group>"; };
 		3219F3B1228B0453003822A6 /* TestImageBlendAnimated.webp */ = {isa = PBXFileReference; lastKnownFileType = file; path = TestImageBlendAnimated.webp; sourceTree = "<group>"; };
+		325E268D25C82BE1000B807B /* TestImageGrayscale.jpg */ = {isa = PBXFileReference; lastKnownFileType = image.jpeg; path = TestImageGrayscale.jpg; sourceTree = "<group>"; };
 		46F21AD7D1692EBAC4D0FF33 /* Pods_SDWebImageWebPCoderTests.framework */ = {isa = PBXFileReference; explicitFileType = wrapper.framework; includeInIndex = 0; path = Pods_SDWebImageWebPCoderTests.framework; sourceTree = BUILT_PRODUCTS_DIR; };
 		808C918B213FD130004B0F7C /* SDWebImageWebPCoderTests.xctest */ = {isa = PBXFileReference; explicitFileType = wrapper.cfbundle; includeInIndex = 0; path = SDWebImageWebPCoderTests.xctest; sourceTree = BUILT_PRODUCTS_DIR; };
 		808C918D213FD131004B0F7C /* SDWebImageWebPCoderTests.m */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.objc; path = SDWebImageWebPCoderTests.m; sourceTree = "<group>"; };
@@ -78,6 +80,7 @@
 		808C9199213FD2B2004B0F7C /* Images */ = {
 			isa = PBXGroup;
 			children = (
+				325E268D25C82BE1000B807B /* TestImageGrayscale.jpg */,
 				808C919A213FD2B2004B0F7C /* TestImageStatic.webp */,
 				808C919B213FD2B2004B0F7C /* TestImageAnimated.webp */,
 				3219F3B1228B0453003822A6 /* TestImageBlendAnimated.webp */,
@@ -154,6 +157,7 @@
 				3219F3B2228B0453003822A6 /* TestImageBlendAnimated.webp in Resources */,
 				808C919D213FD2B2004B0F7C /* TestImageAnimated.webp in Resources */,
 				808C919C213FD2B2004B0F7C /* TestImageStatic.webp in Resources */,
+				325E268E25C82BE1000B807B /* TestImageGrayscale.jpg in Resources */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;
 		};