[antlr-interest] Re: Bug in C# codegen: initializeASTFactory

[slightlynew <gackle at shaw.ca>]

> <scratches-head>Now, just exactly how does one write a simple NUnit 
> test for this report?. Ideas pls people...</scratches-head>
> 
> Micheal

With a code-generation program, you can either write tests to verify 
that the expected code is generated, or tests to verify that the 
generated code behaves as expected.  The second kind of test is 
fairly easy.  In the case of this particular bug, your test would 
initialize a new AST factory, then make sure that factory behaved as 
expected.  The key point is that at first, the test would fail 
(because of the bug), and then pass when the bug is fixed.

Of course, you'd have to write a test grammar to go with this test.  
My approach in a similar situation has been to write a small test 
grammar that is just enough to demonstrate whatever feature I'm 
trying to test, then write the tests to verify that feature.  I keep 
the small test grammars as orthogonal as possible, trying to test one 
thing at a time.  Then there is a higher-level set of acceptance 
tests that involve complex grammars, to make sure that all the 
individual features work together.

As a matter of fact it was tests of this sort that caught the bug.  
My existing tests stopped working when I tried to replace the default 
AST factory with a different one.  By looking at which tests failed, 
it was easy to see that the new factory didn't know about its own 
node types.  The whole process, from breaking the tests to tracking 
down the bug to figuring out a workaround, took about 15 minutes.

Ciao,
Daniel


 

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