Makefile for HUnit tests

Here's a nice idiom for running HUnit tests from a Makefile. Jesse Tov gave me the idea that you can use make's dependencies to test only modules that have changed since the last time you ran the tests. Pick a standard name for each module's tests--tests, say--and make sure it's defined in the first column (since we'll be searching for it with a simple grep). Every time we test a module, we'll touch a dummy file of the same name in some hidden directory--call it .test. So we have two lists of files, the modules of the application and the test dummy files:

SOURCES := $(wildcard *.hs) $(wildcard *.lhs)
TESTS := $(foreach src,$(SOURCES),.test/$(src))

To run the tests, first we collect the list of modified modules and save the names of their tests (Foo.tests, Bar.tests, etc.) in a temporary file .test/args.

.test/%hs: %hs
   @if grep '^tests ' $< > /dev/null 2>&1 ; then \
       touch $@ ; \
       echo $* | sed -e 's/\..*/.tests/' >> .test/args ; \
   fi

Now every time we run the tests, we first make a fresh .test/args file, and then we run GHC with a command-line option to evaluate an expression that runs those tests:

test: teststart $(TESTS)
   @echo ghc Test -e "\"Test.run [ `xargs -a .test/args | tr ' '  ','` ]\""
   @ghc Test -e "Test.run [ `xargs -a .test/args | tr ' ' ','` ]"

teststart:
   @mkdir -p .test
   @$(RM) -f .test/args
   @touch .test/args

It's also useful to have a target that always runs all the tests:

retest: testclean test

testclean:
   $(RM) -rf .test

This assumes the existence of a simple test harness module:

module Test (run) where
import Test.HUnit
run :: [Test] -> IO ()
run ts = (runTestTT $ TestList ts) >> (return ())