If you are testing simple new Thread(runnable).run() You can mock Thread to run the runnable sequentially
For instance, if the code of the tested object invokes a new thread like this
Class TestedClass {
public void doAsychOp() {
new Thread(new myRunnable()).start();
}
}
Then mocking new Threads and run the runnable argument sequentially can help
@Mock
private Thread threadMock;
@Test
public void myTest() throws Exception {
PowerMockito.mockStatic(Thread.class);
//when new thread is created execute runnable immediately
PowerMockito.whenNew(Thread.class).withAnyArguments().then(new Answer<Thread>() {
@Override
public Thread answer(InvocationOnMock invocation) throws Throwable {
// immediately run the runnable
Runnable runnable = invocation.getArgumentAt(0, Runnable.class);
if(runnable != null) {
runnable.run();
}
return threadMock;//return a mock so Thread.start() will do nothing
}
});
TestedClass testcls = new TestedClass()
testcls.doAsychOp(); //will invoke myRunnable.run in current thread
//.... check expected
}