title: mysqltest adding and droping column parallelly
body: <p>I have my own storage engine for mysql and I am trying to writing some test suite for it. Specifically, I want a test which can add and drop columns parallelly for one table, that is, while a thread is adding to table <code>employee</code> columns <code>c1, c2, c3,...,cn</code>, another thread should dropping columns <code>d1, d2, d3,...</code> (assuming there are already those columns). How can I do that.</p>