Android Eclipse Plugin: Instrumentation Test Runner not specified

You're probably missing the uses-library and instrumentation nodes in your AndroidManifest.xml:

<manifest ...>
    <application ...>
        <!-- ... -->
        <uses-library android:name="android.test.runner" />
    </application>
    <instrumentation android:name="android.test.InstrumentationTestRunner"
        android:targetPackage="your.package"
        android:label="your tests label" />
</manifest>

In the Run Configuration you may have Android JUnit Test, if there are any new launch configuration entries inside this, you delete it and then run your application it will run.

NOTE - This is likely to be the solution if you tried to run the test case before adding the correct lines to the manifest as described in the answer from Josef. If you have done this, delete the configuration (which will be complaining that no instrumentation test runner has been specified in its header) and then run it as an Android Junit Test again and it will create a valid configuration picking up the correct stuff that you have added to the manifest (see Josef's answer for this).

One thing I noticed in this discussion that might be tripping some people up is that you need to make sure the "instrumentation" element in your manifest is a child of "manifest" and not of "application." (The examples here are correct, but this easy to mix up.)

http://developer.android.com/guide/topics/manifest/instrumentation-element.html

If you put your instrumentation stuff inside application, it won't be picked up, and your choices in the Eclipse ADT plugin for instrumentation runner may be blank. (But no error is thrown or shown, etc.)