Making Junit tests faster

I had some batch of Junit tests that were taking close to 20 minutes and it was wasteful to wait everytime before checking in code, one trick I found was to use the forkmod="once" property. Using this reduce the time to 5 minute 8 sec.

        <junit tempdir="build" printsummary="on" fork="yes" forkmode="once" haltonfailure="${test.haltonfailure}" failureproperty="tests.failed" showoutput="false">

Earlier Junit was forking a JVM per test and now its doing one for all test so its very fast. Here is some documentation from Junit on this property.

Controls how many Java Virtual Machines get created if you want to fork some tests. Possible values are "perTest" (the default), "perBatch" and "once". "once" creates only a single Java VM for all tests while "perTest" creates a new VM for each TestCase class. "perBatch" creates a VM for each nested and one collecting all nested s. Note that only tests with the same settings of filtertrace, haltonerror, haltonfailure, errorproperty and failureproperty can share a VM, so even if you set forkmode to "once", Ant may have to create more than a single Java VM. This attribute is ignored for tests that don't get forked into a new Java VM. since Ant 1.6.2