The compiler is passed through snaphot build compile and build checks. The so called regression tests check that SDCC itself compiles flawlessly on several host platforms (i386, Opteron, 64 bit Alpha, ppc64, Mac OS X on ppc and i386, Solaris on Sparc) and checks the quality of the code generated by SDCC by running the code for several target platforms through simulators. The regression test suite comprises more than 100 files which expand to more than 500 test cases which include more than 4500 tests. The results of these tests are published daily on SDCC's snapshot page (click on the red or green symbols on the right side of http://sdcc.sourceforge.net/snap.php).
There is a separate document test_suite.pdf http://sdcc.sourceforge.net/doc/test_suite_spec.pdf about the regression test suite.
You'll find the test code in the directory sdcc/support/regression. You can run these tests manually by running make in this directory (or f.e. ''make test-mcs51'' if you don't want to run the complete tests). The test code might also be interesting if you want to look for examples checking corner cases of SDCC or if you plan to submit patches.
The PIC14 port uses a different set of regression tests , you'll find them in the directory sdcc/src/regression.