Sei un figo!

Assigning variables and calculating the result of a math expression are neither new nor interesting ideas.

fixed point 1

Mentioning the types somewhere in the middle of the description is a terrible idea. The initial solution should provide the complete interface of the class instead.

there isn't a lot of katas for training classes

There're many katas which are specifically about working with classes in different languages. Even more katas which use classes only because OOP is cool and imperative code is totally uncool the author decided to write a class with a single static method (or sometimes even worse than that) instead of a regular function for no reason whatsoever. Your statement about "training classes" is especially dumb when you're using Java - an OOP-only language, a language where OOP knowledge is a fundamental requirement for programming.

fixed point 1,2 and 3, about the point 4 you're right, that's not a new idea, but there isn't a lot of katas for training classes and that's very simple

• The speed, distance, and wagons types are not mentioned
• It's not clear what the "assertions" in the description are supposed to mean
• Random tests pass floats to setWagons - wtf?
• Assigning variables and calculating the result of a math expression are neither new nor interesting ideas

a little overkill?