Problem: people don't know how to write test cases

Solution: document the minimum rules in README.md

tests/README.md

+#   Guidelines for tests
+
+Write your test case as if you were writing clean application code. It should be safe to compile on all platforms.
+
+The only include file you should use is `testutil.hpp`. Do not include files from src. Do not use the internal libzmq API or your test case is fair game to be deleted.
+
+If you must write non-portable code, wrap it in #ifdefs to ensure it will compile and run on all systems.
+
+Note that testutil.hpp includes platform.h. Do not include it yourself as it changes location depending on the build system and OS.
+
+