Provide convenience methods in FXComponentTest to load fxml file

[MarceloRuiz]

The three most common scenarios I can think off for using FXComponentTest are:

• Test a programatically created component (as seen in the FX Test example)

• Test a component initialized from a FXML file, instantiated with the controller class (if defined in the fxml file, obviously).

• Test a component initialized from a FXML file, instantiated with a mocked controller.

For the last 2 scenarios, FXComponentTest could easily provide helper methods. The following code could be added to FXComponentTest (and is compatible with issues #17 and #19):

private static final Pattern FXML_CONTROLLER_PATTERN = Pattern.compile("\\sfx:controller=\\\".+\\\"");

protected O loadFromFXML(final String fxmlFileName) throws IOException {
	final URL location = getClass().getResource(fxmlFileName);		
	final FXMLLoader loader = new FXMLLoader(location);
	
	return loader.load();
}

protected O loadFromFXML(final String fxmlFileName, final Object controller) throws IOException, URISyntaxException {	
	final FXMLLoader loader = new FXMLLoader();
	
	loader.setController(controller);
	return loader.load(getControllerStrippedFxml(fxmlFileName));
}	

private InputStream getControllerStrippedFxml(final String fxmlFileName) throws IOException, URISyntaxException {
	final ByteArrayOutputStream fileContent = new ByteArrayOutputStream();
	final StringBuffer strippedContent = new StringBuffer();
	final Matcher matcher;
	
	try (InputStream is = getClass().getResource(fxmlFileName).openStream()) {
		byte[] chunk = new byte[4096];
        	int bytesRead;
        
       		 while ((bytesRead = is.read(chunk)) > 0) {
        		fileContent.write(chunk, 0, bytesRead);
	        }
	}

	matcher = FXML_CONTROLLER_PATTERN.matcher(fileContent.toString());

	while (matcher.find()) {
		matcher.appendReplacement(strippedContent, "");
	}
	matcher.appendTail(strippedContent);
	return new ByteArrayInputStream(strippedContent.toString().getBytes());
}

The above code would allow a user of FXComponentTest create a component just just a few lines of code. For example, suppose I want to test a Pane defined by a fxml file inserted into a BorderPane:

@RunWith(FXRunner.class)
public class MyViewTest extends FXComponentTest<BorderPane, Pane> {

        //other methods here

	@Override
	protected Pane createComponent(final BorderPane parent)  throws IOException {
		final Pane pane = loadFromFXML("myView.fxml");
		
		parent.setCenter(pane);
		return pane;
	}
}

If I want to test the view with a custom controller (mock/stub/spy) then the class would look like:

@RunWith(FXRunner.class)
public class MyViewTest extends FXComponentTest<BorderPane, Pane> {

        final MyController controller = //controller creation here

        //other methods here

	@Override
	protected Pane createComponent(final BorderPane parent)  throws IOException, , URISyntaxException {
		final Pane pane = loadFromFXML("myView.fxml", controller);
		
		parent.setCenter(pane);
		return pane;
	}
}

The added benefit of easily creating a component with a custom controller is that test would be really easy if the user decides to use the PMVC pattern for designing the views.