[antlr-interest] gUnit for v4?

Terence Parr parrt at cs.usfca.edu
Sun Apr 15 14:36:02 PDT 2012


I started down the path of building the new version of gUnit for v4, but I'm beginning to question its value for the new version. Because I am pooh-poohing putting actions directly within a grammar, grammar can only yield parse trees. and looks nice to be able to say:

	"1"		-> (expr 1)
	"1+2"	-> (expr (expr 1) + (expr 2))

but so what? all that did was confirm that the parser generated by ANTLR works correctly. it's not telling you anything you didn't know by looking at the grammar.

In the old days we used to build ASTs and so we needed to check the structure. That need is no longer here. Also, these rules don't generate output and so we can't check input to output translation.

What it comes down to is this: we really need functional testing not unit testing for language applications, unless of course each rule returns a string that the translation of the input some phrase or something. But, it's just as easy to write calls to assertEquals() saying that input x should yield input y. If we are doing something other than generating output, such as building up a data structure, then we really do need to manually check that the data structure is solid given some input.

I'm trying to find a flaw in my logic. Is there something I'm missing about testing grammars? In v4, they will give you exactly what you want, unless there is a bug in ANTLR. But that's my problem not yours.

If we can't find a major benefit, then we should avoid introducing another moving part to the ANTLR ecosystem.


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