There are several different types of dwarfs. The two most commonly mentioned are the snorters and the long heads. There are also proportionate dwarfs, which is what your calf appears to be. There is a test for the "Long head" dwarf, but I do not believe a test has yet been developed for the snorter or proportionate dwarfs (often referred to as "itty bittys"). The test you are planning will most likely come back negative, since this does not resemble the long headed dwarfs, but that does not mean the cow and bull aren't dwarf carriers for a different type of dwarfism.
I would not worry too much about it. It is not life threatening to either the cow or the calf and we will probably never eliminate all forms of dwarfism. I would just stay away from excessive inbreeding with those animals.