Fast development => test database cloning

Goal:
Before running tests I want test db to be development db + some
fixtures.

Problem:
Since application is about statistical computations, development db is
large.
Standard db=>yml=>db approach is to slow.

Question:
What is the fastest way to create test database from development
database?
Maybe some magic MySQL command? And how to integrate new way of test
database generation it into rake test “processing pipe”?

Thanks in advance

A magic rails command:

rake db:test:clone