Smalltalk tiny exercise for TDD newbies

Done in course:

Create the category Exercise in the Browser. All classes you create will be placed in this category.

Implement the class Operation (using Test-Driven Development) which should work like this:

1. a := Operation new.
   a result.
   

   Should return 0.

2. b := Operation new.
   b add: 2.
   b add: 3.
   b result.
   

   Should return 5.

3. Operation new
     add: 2;
     add: 4;
     divideBy: 2;
     result.
   

   Should return 3.

Add the message Operation>>#multiplyBy by yourself.