utils: fix ColorToUint

as a side-effect I've added an unittest for UintToColor

Utils.go

@@ -231,7 +231,10 @@ func ColorToUint(col color.Color) uint32 {
 	r, g, b, a := col.RGBA()
 	mask := uint32(0xff)
 
-	return r&mask<<24 + g&mask<<16 + b&mask<<8 + a&mask
+	return r&mask +
+		g&mask<<8 +
+		b&mask<<16 +
+		a&mask<<24
 }
 
 // UintToColor converts uint32 of form 0xRRGGBB into color.RGBA.

Utils_test.go

@@ -107,3 +107,20 @@ func Test_Assert(t *testing.T) {
 		})
 	}
 }
+
+func TestUintToColor(t *testing.T) {
+	tests := []struct {
+		name string
+		col  uint32
+		want *color.RGBA
+	}{
+		{"full red full alpha", 0xFF0000FF, &color.RGBA{R: 255, G: 0, B: 0, A: 255}},
+		{"full red 0 alpha", 0xFF000000, &color.RGBA{R: 255, G: 0, B: 0, A: 0}},
+		{"full green", 0x00FF00FF, &color.RGBA{R: 0, G: 255, B: 0, A: 255}},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			assert.Equalf(t, tt.want, UintToColor(tt.col), "UintToColor(%v)", tt.col)
+		})
+	}
+}