How should I unit test a code-generator?

Posted by jkp on Stack Overflow See other posts from Stack Overflow or by jkp
Published on 2008-08-14T13:59:21Z Indexed on 2010/05/19 23:20 UTC
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This is a difficult and open-ended question I know, but I thought I'd throw it to the floor and see if anyone had any interesting suggestions.

I have developed a code-generator that takes our python interface to our C++ code (generated via SWIG) and generates code needed to expose this as WebServices. When I developed this code I did it using TDD, but I've found my tests to be brittle as hell. Because each test essentially wanted to verify that for a given bit of input code (which happens to be a C++ header) I'd get a given bit of outputted code I wrote a small engine that reads test definitions from XML input files and generates test cases from these expectations.

The problem is I dread going in to modify the code at all. That and the fact that the unit tests themselves are a: complex, and b: brittle.

So I'm trying to think of alternative approaches to this problem, and it strikes me I'm perhaps tackling it the wrong way. Maybe I need to focus more on the outcome, IE: does the code I generate actually run and do what I want it to, rather than, does the code look the way I want it to.

Has anyone got any experiences of something similar to this they would care to share?

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