[Nmock-general] Proposal for a change.

[Steve F. <st...@m3...>]

We've been using the NMock constraints and have come across a little 
problem. We're using it for testing the contents of DOM elements by 
driving IExplorer through its API. We've written some extra constraints 
that match parts of an element, which works fine, but we means we have a 
hard time printing meaningful error messages because it's only the 
constraint that extracts the final value to check, we can't tell from 
the containing assertion. For example:

   IConstraint constraint = new IElementTextEquals("some text");

   Assert("Expected " + constraint.Message + " got " + ielement,
          constraint.Eval(ielement));

will only show the class of ielement when it fails. We can't find its 
text contents.

The object that /does/ know the actual value is the constraint, so that 
seems like the right object to ask. I can see two ways of doing this:

- add a method, say,
     object TestValue(object actual)
   that unpacks the value you want to test against, in this case the 
element text,
   by default the 'actual' object.

- hang on to the the last test value during the Eval and make it 
available via a LastValue property.

Thoughts?

S.