The Plan A

In object-oriented programming, mock objects are simulated objects that mimic the behavior of real objects in controlled ways

Wikipedia

Use mocks when you to :

• improve test performances.
• Remove dependencies of external systems.
• control the behavior of a method.

Via MockFight

This is a 5 minutes introduction to create a core patch to Rubinius.

1. Write a core library patch to Rubinius is really easy. First we need to decide what we want to write. Run the specs and find a bug, or write your own specs. Im going to write my own spec. I decide to implement the missing spec hypotenuse form Math Module
2. A bit of Test driven development :
   1. Find the math specs file : RUBINIUS_HOME/spec/core/math_spec.rb
   2. Write the spec :
      1. create the describe :

         describe "Math#hypot" doend

      2. Add the basic cases :

         it "return x**2+y**2" do
            Math.hypot(0,0).should_be_close(0.0,TOLERANCE)Math.hypot(2,10).should_be_close( 10.1980390271856 ,TOLERANCE)
            Math.hypot(5000,5000).should_be_close(7071.06781186548 ,TOLERANCE)
            Math.hypot(0.0001,0.0002).should_be_close(0.000223606797749979,TOLERANCE)
            Math.hypot(-2,-10).should_be_close(Math.hypot(2,10),TOLERANCE)
            Math.hypot(2,10).should_be_close(Math.hypot(10,2),TOLERANCE)
         end

      3. Add exceptional cases :

          it "raise an ArgumentError exception if the argument are  the wrong type" do
            should_raise(ArgumentError){Math.hypot("test","test2")}
         end
          it "raise an TypeError exception if the argument is nill" do
           should_raise(ArgumentError){Math.hypot(nil)}
         end 

   3. run the specs. ruby spec/core/math_spec.rb. Umm 3 fails
3. Ok, lets coding
   1. Find the math module : RUBINIUS_HOME/kernel/core/math.rb
   2. Write the method

      1. def hypot(x,y)
             sqrt(x**2 + y**2);
         end

      2. rebuild the core: rake build:core
      3. run the test again … ummm two fails. not so bad.
   3. Lets code again :
      1. The method :

           def hypot(x,y)     raise ArgumentError unless x.kind_of? Numeric or y.kind_of? Numericsqrt(x**2 + y**2)end

      2. rebuild the core
      3. re run the specs … 0 fails !!
      4. Thats all.
   4. No !! thats not al. As Tony Targonski point in the comments we have a bug. Ok lets write a case for the bug.

      1. it "raise an ArgumentError exception if the argument are  the wrong type" do
         
           should_raise(ArgumentError){Math.hypot("test","test2")}
         end/pre>
         

      2. run again the specs 1 fail !! ohhhh, We have a bug. Dont live with broken windows.
      3. Replace the "or" with "and"
      4. re run the spec.... 0 fails again. great just in time to go home.