anchor.diff:  | `is_false` | evaluates to false
   | `is_null` | equals null
   | `is_non_null` | is a non null value
  +| `is_not_null` | d:o
   ||
   | `is_equal_to(value)` | '== value'
   | `is_not_equal_to(value)` | '!= value'
  
positive.code: are empty. (You will get strange errors if you don't!)
  
  NOTE: We are using the name "Cgreen" as the SUT in these first
  examples, as if *Cgreen* itself was the object or class we wanted to
  test or describe.
  
  I am assuming you have the *Cgreen* folder in the include search
  
negative.code: assertions accept anything that can be cast to `intptr_t` and simply
  perform an `==` operation. The string comparisons are slightly
  different in that they use the `<string.h>` library function
  `strcmp()`.  If you use `is_equal_to()` with `char *` pointers then it is the value of the pointers themselves that has to be the same, i.e. the
  pointers have to point at the same string for the test to pass.
  
  A cautionary note about the constraints is that you cannot use C/C++
  string literal concatenation (like `"don't" "use" "string"
  "concatenation"`) in the parameters to the constraints. If you do, you
  will get weird error messages about missing arguments to the
  constraint macros. This is caused by the macros using argument strings
  to produce nice failure messages.
  