Add in fizzbuzz files with minitest running.
Return the correct numbers based on initialization.
Properly substitute Fizz
Properly substitute Buzz
Clean up the tests a bit.
Implement fizzbuzz substitution.
Make it easier to read

Using a private method gives a name to the modulo operation.
Use the fact that if statements return a value.

This makes is a bit easier to see what the substitutions are.
Hide this away in a private method with a name.

Again we have a concept of what this is.
No need for the intermediate variable for clarity.