Wait for Platform.RunLater in a unit test

Question

I have a presentation class storing an XYChart.Series object and updating it by observing the model. The Series updating is done by using Platform.runLater(...)

I want to unit-test this, making sure the commands in runLater are performed correctly. How do I tell the unit-test to wait for the runLater commands to be done? Right now all I do is Thread.Sleep(...) on the test-thread to give the FXApplicationThread the time to complete, but that sounds stupid.

Answer 1

The way I solved it is as follows.

1) Create a simple semaphore function like this:

public static void waitForRunLater() throws InterruptedException {
    Semaphore semaphore = new Semaphore(0);
    Platform.runLater(() -> semaphore.release());
    semaphore.acquire();

}

2) Call waitForRunLater() whenever you need to wait. Because Platform.runLater() (according to the javadoc) execute runnables in the order they were submitted, you can just write within a test:

...
commandThatSpawnRunnablesInJavaFxThread(...)
waitForRunLater(...)
asserts(...)`

which works for simple tests