How does GHC's testsuite work?

[Sébastien Hinderer]

Dear all,

I am a member of OCaml's developement team. More specifically, I am
working on a test-driver for the OCaml compiler, which will be part of
OCaml's 4.06 release.

I am currently writing an article to describe the tool and its
principles. In this article, I would like to also talk about how other
compilers' testsuites are handled and loking how things are done in GHC
is natural.

In OCaml, our testsuite essentially consist in whole programs that
we compile and run, checking that the compilation and execution results
match the expected ones.

>From what I could see from GHC's testsuite, it seemed to me that it uses
Python to drive the tests. I also understood that the testsuite has
tests that are more kind of unit-tests, in the .T file. Am I correct
here? Or do you guys also have whole program tests?
If you do, how do you compile and run them?

Any comment / hint on this aspect of the test harness' design would be
really helpful.

Many thanks in advance,

Sébastien.