I was reading about the definition of electric field. It said that electric field at a point due to a source charge is the force exerted by it on another charge placed at that point divided by the magnitude of charge placed at that point. But, obviously, if we place any finite charge in electric filed, it will disturb the original source charge and thereby it will change the value of electric field at that point. So, when defining electric field we often use the term 'test charge' which is infinitesimally small so that it does not disturb the original charge. Mathematically we represent it as lim F/q as q tends to zero. But we cannot talk about such a charge given that charge is quantized. The smallest building block of charge which I'm aware of is a quark. And, it is still something finite so that it will disturb the source charge. Then, how can we talk about charges which are as close to zero as possible? Doesn't this seem like implying that charge distributions are continuous and charge can take any value like mass?