To be able to see the level of coverage with the current test suite,
do the following:

  - Make sure gcov is installed
  - Compile the MySQL distribution with BUILD/compile-pentium-gcov (if your
    machine does not have a pentium CPU, hack this script, or just live with
	the pentium-specific stuff)
  - In the mysql-test directory, run this command: ./mysql-test-run -gcov
  - To see the level of coverage for a given source file:
     grep source_file_name /tmp/gcov.out
  - To see which lines are not yet covered, look at source_file_name.gcov in
    the source tree. Then think hard about a test case that will cover those
    lines, and write one!