What is this bump on dog?

My dog got this bump a few days ago and I wanted to know what it COULD be. It is one single bump  and is crusty with yellow crust . It doesn’t seem to be bothering him much .

Hello!  This is slightly out of context- I trust that it's a dog?  Where abouts in the dog is this?  If this is on the side of the face, it could be one of the normal specialised hair follicles at the base of the whisker, but it could also be a view of one of the small, 'extra' teats for example. However, if this is a new lump then it ought to be checked by your vet.  In this case, we would be wondering whether it was inflammatory, cystic or cancerous (including benign cancers such as histicytoma) as an early question and histology may be needed. Please do let me know how you get on.

For 'tests' please read 'teats'!