document new test framework

test/README

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+-----------
+ For: User
+-----------
+
+The following make variables may help you in testing:
+ - UCLIBC_ONLY  - only run tests against uClibc
+ - GLIBC_ONLY   - only run tests against glibc
+ - COMPILE_ONLY - just build the tests, don't run them
+ - V / VERBOSE  - run tests with a lot of output
+
+So, to just run the uClibc tests, try this:
+make check UCLIBC_ONLY=1
+
+----------------
+ For: Developer
+----------------
+
+The structure of this test system is:
+ test/                 toplevel dir containing common test code
+ test/Rules.mak        Common build code
+ test/Test.mak         Runtime test make code
+ test/subdir/          code specific to a subsystem is stored in a subdir
+ test/subdir/Makefile  describe the tests to run
+ test/subdir/*.c       the tests
+
+Each subdir Makefile must define the TESTS variable and include the
+toplevel Test.mak file:
+TESTS := foo
+include ../Test.mak
+Each test must use a similar .c name; so the "foo" test needs a "foo.c".
+
+Additionally, the following options further control specific test behavior:
+CFLAGS_foo    := extra cflags to use to compile test
+DODIFF_foo    := compare the output of the glibc and uClibc tests (see below)
+LDFLAGS_foo   := extra ldflags to use to link test
+OPTS_foo      := extra options to pass to test
+RET_foo       := expected exit code of test; default is 0
+WRAPPER_foo   := execute stuff just before test
+
+Or to control all tests in a subdir:
+EXTRA_CLEAN   := extra files to remove in the clean target
+EXTRA_CFLAGS  := -DFOO
+EXTRA_LDFLAGS := -lpthread
+OPTS          := 
+WRAPPER       := 
+
+If you want to compare the output of a test with known good output, then just
+create a local file named "foo.out.good" and the output generated by the test
+"foo" will be automatically stored in "foo.out" and compared to "foo.out.good".