add miscellaneous tests

also fix minor bug in detecting content type for content less than 512
bytes.

transform_test.go

@@ -91,6 +91,7 @@ func TestCropParams(t *testing.T) {
 		{Options{CropX: 50, CropY: 100, CropWidth: 100, CropHeight: 150}, 50, 100, 64, 128},
 		{Options{CropX: -50, CropY: -50}, 14, 78, 64, 128},
 		{Options{CropY: 0.5, CropWidth: 0.5}, 0, 64, 32, 128},
+		{Options{Width: 10, Height: 10, SmartCrop: true}, 0, 0, 64, 64},
 	}
 	for _, tt := range tests {
 		want := image.Rect(tt.x0, tt.y0, tt.x1, tt.y1)
@@ -148,6 +149,17 @@ func TestTransform(t *testing.T) {
 	}
 }
 
+func TestTransform_InvalidFormat(t *testing.T) {
+	src := newImage(2, 2, red, green, blue, yellow)
+	buf := new(bytes.Buffer)
+	png.Encode(buf, src)
+
+	_, err := Transform(buf.Bytes(), Options{Format: "invalid"})
+	if err == nil {
+		t.Errorf("Transform with invalid format did not return expected error")
+	}
+}
+
 // Test that each of the eight EXIF orientations is applied to the transformed
 // image appropriately.
 func TestTransform_EXIF(t *testing.T) {