anchor.diff:  that´ to `ensure that´, makes a huge difference in thinking, and also
   very often in quality of the resulting code.
   
  -The SUT - Subject Under Test
  -~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  +
  +=== The SUT - Subject Under Test
   
   Since BDD talks about behaviour, there has to be something that we can
   talk about as having the wanted behaviour. This is usually called the
  
positive.code: form for asserting boolean expressions (`assert_that(0 == 1);`).
  
  [[tdd_with_cgreen]]
  Five Minutes Doing TDD with Cgreen
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  
  For a more realistic example we need something to test. We'll pretend
  that we are writing a function to split the words of a sentence in
  
negative.code: 
  That was pretty straight forward. Let's do something more interesting.
  
  === What are Mock Functions?
  
  The next example is a more realistic extension of our previous
  attempts. As in real life we first implement something basic and then
  