Download and compile Dovecot v2.2 sources (older versions won't work). imaptest uses its library functions. Dovecot doesn't have any external dependencies.
Get the latest nightly snapshot from http://dovecot.org/nightly/dovecot-latest.tar.gz
Compiling goes the usual way: ./configure && make (there's no need for make install)
imaptest configure wants to find dovecot-config, which is created by running (and finishing) make
If you want to avoid having to install shared Dovecot libraries, you can use ./configure --without-shared-libs
Download and compile http://dovecot.org/nightly/imaptest/imaptest-latest.tar.gz
./configure --with-dovecot=../dovecot-20080611 && make
--with-dovecot=<path> parameter is used to specify path to Dovecot v2.2 sources' root directory.
Either make install or run src/imaptest directly.
Also note that you need a test mbox file where messages are uploaded from.
You may want to modify the default configuration from #defines in src/settings.h. This isn't required, but if you run imaptest often, this way you don't have to give the same parameters every time.
You can also get imaptest sources from Github.
Run autoreconf -i to build configure script.