Although you can run test through Eclipse and via Ant, running them directly though adb is often the best option since
when you're running them on a build server Eclipse's method won't be available to you, and;
the default ant 'test' target doesn't take into account non-standard source directories or non-standard test runners for example.
It's simply enough using adb, as soon as you've installed the test project on your device/emulator:
adb shell am instrument -w your.test.project.package/android.test.InstrumentationTestRunner
The -w tag tells it to wait and print out the results. The package is what you've defined in the AndroidManifest.xml in your Android test project. The text after that is the test runner, the default one in this case.