1. override
bool debugAssertIsValid()

In checked mode, throws an exception if the object is not in a valid configuration. Otherwise, returns true.

This is intended to be used as follows:

  assert(myDecoration.debugAssertIsValid());

Source 

@override
bool debugAssertIsValid() {
  assert(swatch != null
      && swatch[_lightShade] != null
      && swatch[_darkShade] != null
      && textColor != null
      && style != null
      && _position != null
      && _position.isFinite
      && _opacity != null
      && _opacity >= 0.0
      && _opacity <= 1.0
      && margin != null);
  return true;
}