Another reason to love Groovy.

SwingBuilderTestCaseUtils.groovy

@BeforeClass void setup() {
    SwingUtilities.metaClass.static.invokeLater = { Runnable runnable ->
        runnable.run()
    }
    
    Thread.metaClass.static.start = { Runnable runnable ->
        runnable.run()
    }    
}

@AfterClass void tearDown() {
    // rollback metaclass changes
    GroovySystem.metaClassRegistry.removeMetaClass(Thread.class)
    GroovySystem.metaClassRegistry.removeMetaClass(SwingUtilities.class)    
}

@Test void buttonClickedTriggersFocus() {
    // do UI testing stuff
}