Capture screenshot on failing SWTBot tests

Sometimes functional tests fail. If they do, I not only want to see the test and the error message, I also want a screenshot of the application in the state during the failing test.

I was astonished to find nothing in the SWTBot code or documentation that suggests how to automatically capture a screenshot when a SWTBot test fails. This is why I came up with a JUnit4 Rule that does this.

In your SWTBot test class include the field

public class MyTest {
  @Rule
  public CaptureScreenshotOnFailure screenshot = new CaptureScreenshotOnFailure();
  
  @Test public void mytestmethod() {
    SWTBot bot = new SWTBot(...);
    // swtbot clicks and types
  }

So, if now mytestmethod fails, a screenshot will be put in the current directory with the name mypackage.MyTest.mytestmethod.png

This is the rule, put it somewhere where your test classes can access it:

import org.eclipse.swtbot.eclipse.finder.SWTWorkbenchBot;
import org.junit.rules.MethodRule;
import org.junit.runners.model.FrameworkMethod;
import org.junit.runners.model.Statement;

public class CaptureScreenshotOnFailure implements MethodRule {
	public final Statement apply(final Statement base,
			final FrameworkMethod method, Object target) {
		return new Statement() {
			@Override
			public void evaluate() throws Throwable {
				try {
					base.evaluate();
				} catch (Throwable onHold) {
					String fileName = constructFilename(method);
					new SWTWorkbenchBot().captureScreenshot(fileName);
					throw onHold;
				}
			}

			private String constructFilename(final FrameworkMethod method) {
				return "./"
						+ method.getMethod().getDeclaringClass()
								.getCanonicalName() + "."
						+ method.getName() + ".png";
			}
		};
	}
}

I think this makes writing tests with SWTBot more comfortable. Do you see ways to improve this rule?