TicklingJavawithaFeather.PDF

Electronic Notes in Theoretical Computer Science 238 (2009) 3–16 /locate/entcs Tickling Java with a Feather Tristan O.R. Allwood1 Susan Eisenbach2 Department of Computing Imperial College London United Kingdom Abstract Fragments of mainstream programming languages are formalised in order to show desirable prop- erties of their static semantics. We ask if said formalisms could also be used to define a test suite for the mainstream programming language in question, and what the utility of such a suite would be. In this work, we present our findings from testing Java with Featherweight Java (FJ). We take the syntax and binding structure of FJ to define an instance space of non-isomorphic test programs and implementations of FJ type checkers to provide oracles for our tests, to ensure the mainstream implementation conforms with the expectations of FJ. Using these, we evaluate (using code coverage techniques) how much of the Sun OpenJDK javac can be tested by FJ. Keywords: Featherweight Java, Tests, Semantics, Oracles 1 Introduction Writing compilers and type checkers is hard. In addition to the sheer quan- tity of code, the implementation may be complicated by the desire to produce code that is efficient and fast. The languages compilers are processing are ever-increasingly complicated, with sophisticated type rules, and many possi- ble obscure corner cases. There are also complications with possibly several intermediate representations being used inside the compiler, each with their own invariants and properties. 1 Email: tristan.allwood@imperial.ac.uk 2 E