Put test1.js and test2.js into a tests/ directory, then run the suite:
$ casperjs test tests/ --pre=pre.js --includes=inc.js --post=post.js
Test file: /Users/nperriault/tmp/pre-inc/pre.js
Hey, I'm executed before the suite.
Test file: /Users/nperriault/tmp/pre-inc/tests/test1.js
# this is test 1
Hi, I've been included.
PASS Subject is strictly true