In Junit 5 how can I call a test class method from an extension?

Question

In Junit 5 I'm trying to get a test class method to run from an extension. I'm using the Junit 5 extension interface, TestWatcher, and overriding the testFailed() method.

The test class method has the instantiated browser and annotation for attaching to Allure. And my takeScreenshot method relies on the browser and a testName string from the test class to run correctly.

package utils;

public class ScreenshotOnFailureExtension implements TestWatcher{
    @Override
    public void testFailed(ExtensionContext context, Throwable cause) {
        try {
            Object clazz = context.getRequiredTestInstance();
            Method takeScreenshot = clazz.getClass().getMethod("takeScreenshot");
            takeScreenshot.setAccessible(true);
            Object test = clazz.getClass().getConstructor().newInstance();
            takeScreenshot.invoke(test);
        } catch (Exception e) {
            e.printStackTrace();
        } 
}

Answer 1

In Junit 5 I'm trying to get a test class method to run from an extension. I'm using the Junit 5 extension interface, TestWatcher, and overriding the testFailed() method.

The purpose of this extension is to take a screen shot on failure in the test class's Selenium WebDriver browser and attach it to that test's Allure report. The test class method has the instantiated browser and annotation for attaching to Allure. And my takeScreenshot method relies on the browser and a testName string from the test class to run correctly.

package utils;

public class ScreenshotOnFailureExtension implements TestWatcher{
    @Override
    public void testFailed(ExtensionContext context, Throwable cause) {
        try {
            Object clazz = context.getRequiredTestInstance();
            Method takeScreenshot = clazz.getClass().getMethod("takeScreenshot");
            takeScreenshot.setAccessible(true);
            Object test = clazz.getClass().getConstructor().newInstance();
            takeScreenshot.invoke(test);
        } catch (Exception e) {
            e.printStackTrace();
        } 
}

And the code in my test class is something like this:

package tests;

@ExtendWith(ScreenshotOnFailureExtension.class)
public class MyTest implements Config {
    public WebDriver driver;
    public String testName;

//bunch of Junit5 annotations with functions to initialize above variables omitted...

    //take a screen shot
    public void takeScreenshot() {
        System.out.println("Taking screenshot.");
        byte[] srcFile=((TakesScreenshot)driver).getScreenshotAs(OutputType.BYTES);
        saveScreenshot(srcFile, testName+ ".png");
    }
    
    //this attaches screenshot to an allure test result
    @Attachment(value = "{testName}", type = "image/png")
    public byte[] saveScreenshot(byte[] screenShot, String testName) {
        System.out.println("Attaching screenshot to Allure report");
        return screenShot;
    }
}

The above test class is able to take a screen shot correctly when calling from @AfterEach in the test method. But I only want to take it on a failure.

When I run the test it calls takeScreenshot, but then gives an exception while executing it:

Taking screenshot.java.lang.reflect.InvocationTargetException

at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.base/java.lang.reflect.Method.invoke(Method.java:566) at utils.ScreenshotOnFailureExtension.testFailed(ScreenshotOnFailureExtension.java:49) at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.lambda$nodeFinished$14(TestMethodTestDescriptor.java:299) at org.junit.jupiter.engine.descriptor.MethodBasedTestDescriptor.lambda$invokeTestWatchers$3(MethodBasedTestDescriptor.java:134) at java.base/java.util.ArrayList.forEach(ArrayList.java:1540) at org.junit.jupiter.engine.descriptor.MethodBasedTestDescriptor.invokeTestWatchers(MethodBasedTestDescriptor.java:132) at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.nodeFinished(TestMethodTestDescriptor.java:290) at org.junit.jup iter.engine.descriptor.TestMethodTestDescriptor.nodeFinished(TestMethodTestDescriptor.java:65) at org.junit.platform.engine.support.hierarchical.NodeTestTask.reportCompletion(NodeTestTask.java:176) at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:89) at java.base/java.util.ArrayList.forEach(ArrayList.java:1540) at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:38) at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:143) at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73) at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:129) at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137) at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursi vely$8(NodeTestTask.java:127) at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73) at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:126) at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:84) at java.base/java.util.ArrayList.forEach(ArrayList.java:1540) at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:38) at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:143) at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73) at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:129) at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137) at org.junit.platform.engine.support.hiera rchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:127) at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73) at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:126) at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:84) at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.submit(SameThreadHierarchicalTestExecutorService.java:32) at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor.execute(HierarchicalTestExecutor.java:57) at org.junit.platform.engine.support.hierarchical.HierarchicalTestEngine.execute(HierarchicalTestEngine.java:51) at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:108) at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:88) at org.junit.platform.laun cher.core.EngineExecutionOrchestrator.lambda$execute$0(EngineExecutionOrchestrator.java:54) at org.junit.platform.launcher.core.EngineExecutionOrchestrator.withInterceptedStreams(EngineExecutionOrchestrator.java:67) at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:52) at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:96) at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:75) at org.eclipse.jdt.internal.junit5.runner.JUnit5TestReference.run(JUnit5TestReference.java:89) at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:41) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:541) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:763) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:463) at org.eclipse.jdt.internal.junit.runner.RemoteTest Runner.main(RemoteTestRunner.java:209) Caused by: java.lang.NullPointerException at tests.Base.takeScreenshot(Base.java:240) ... 49 more

You can see my logging statement being output before the NullPointerException caused by the next line of code in that method (referencing the driver from the test instance). Is there a correct way to trigger the existing test instance's takeScreenshot() method in context?

OR

If there is a simpler way to take a screen shot on failure directly in the test's @AfterEach method, PLEASE let me know. Seems like a pretty basic use case. :)

Answer 2

In Junit 5 I'm trying to get a test class method to run from an extension. I'm using the Junit 5 extension interface, TestWatcher, and overriding the testFailed() method.

The purpose of this extension is to take a screen shot on failure in the test class's Selenium WebDriver browser and attach it to that test's Allure report. The test class method has the instantiated browser and annotation for attaching to Allure. And my takeScreenshot method relies on the browser and a testName string from the test class to run correctly.

package utils;

public class ScreenshotOnFailureExtension implements TestWatcher{
    @Override
    public void testFailed(ExtensionContext context, Throwable cause) {
        try {
            Object clazz = context.getRequiredTestInstance();
            Method takeScreenshot = clazz.getClass().getMethod("takeScreenshot");
            takeScreenshot.setAccessible(true);
            Object test = clazz.getClass().getConstructor().newInstance();
            takeScreenshot.invoke(test);
        } catch (Exception e) {
            e.printStackTrace();
        } 
}

And the code in my test class is something like this:

package tests;

@ExtendWith(ScreenshotOnFailureExtension.class)
public class MyTest implements Config {
    public WebDriver driver;
    public String testName;

//bunch of Junit5 annotations with functions to initialize above variables omitted...

    //take a screen shot
    public void takeScreenshot() {
        System.out.println("Taking screenshot.");
        byte[] srcFile=((TakesScreenshot)driver).getScreenshotAs(OutputType.BYTES);
        saveScreenshot(srcFile, testName+ ".png");
    }
    
    //this attaches screenshot to an allure test result
    @Attachment(value = "{testName}", type = "image/png")
    public byte[] saveScreenshot(byte[] screenShot, String testName) {
        System.out.println("Attaching screenshot to Allure report");
        return screenShot;
    }
}

The above test class is able to take a screen shot correctly when calling from @AfterEach in the test method. But I only want to take it on a failure.

When I run the test it calls takeScreenshot, but then gives an exception while executing it:

Taking screenshot.java.lang.reflect.InvocationTargetException

at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.base/java.lang.reflect.Method.invoke(Method.java:566) at utils.ScreenshotOnFailureExtension.testFailed(ScreenshotOnFailureExtension.java:49) at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.lambda$nodeFinished$14(TestMethodTestDescriptor.java:299) at org.junit.jupiter.engine.descriptor.MethodBasedTestDescriptor.lambda$invokeTestWatchers$3(MethodBasedTestDescriptor.java:134) at java.base/java.util.ArrayList.forEach(ArrayList.java:1540) at org.junit.jupiter.engine.descriptor.MethodBasedTestDescriptor.invokeTestWatchers(MethodBasedTestDescriptor.java:132) at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.nodeFinished(TestMethodTestDescriptor.java:290) at org.junit.jup iter.engine.descriptor.TestMethodTestDescriptor.nodeFinished(TestMethodTestDescriptor.java:65) at org.junit.platform.engine.support.hierarchical.NodeTestTask.reportCompletion(NodeTestTask.java:176) at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:89) at java.base/java.util.ArrayList.forEach(ArrayList.java:1540) at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:38) at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:143) at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73) at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:129) at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137) at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursi vely$8(NodeTestTask.java:127) at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73) at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:126) at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:84) at java.base/java.util.ArrayList.forEach(ArrayList.java:1540) at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:38) at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:143) at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73) at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:129) at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137) at org.junit.platform.engine.support.hiera rchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:127) at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73) at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:126) at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:84) at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.submit(SameThreadHierarchicalTestExecutorService.java:32) at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor.execute(HierarchicalTestExecutor.java:57) at org.junit.platform.engine.support.hierarchical.HierarchicalTestEngine.execute(HierarchicalTestEngine.java:51) at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:108) at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:88) at org.junit.platform.laun cher.core.EngineExecutionOrchestrator.lambda$execute$0(EngineExecutionOrchestrator.java:54) at org.junit.platform.launcher.core.EngineExecutionOrchestrator.withInterceptedStreams(EngineExecutionOrchestrator.java:67) at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:52) at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:96) at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:75) at org.eclipse.jdt.internal.junit5.runner.JUnit5TestReference.run(JUnit5TestReference.java:89) at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:41) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:541) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:763) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:463) at org.eclipse.jdt.internal.junit.runner.RemoteTest Runner.main(RemoteTestRunner.java:209) Caused by: java.lang.NullPointerException at tests.Base.takeScreenshot(Base.java:240) ... 49 more

You can see my logging statement being output before the NullPointerException caused by the next line of code in that method (referencing the driver from the test instance). Is there a correct way to trigger the existing test instance's takeScreenshot() method in context?

OR

If there is a simpler way to take a screen shot on failure directly in the test's @AfterEach method, PLEASE let me know. Seems like a pretty basic use case. :)

Answer 3

The solution ended up looking like this. You could add other actions here for a Selenium test because this executes just before test tear-down.

If you are using Junit5 for Selenium testing you can use the AfterTestExecutionCallback so that the RequiredTestInstance contains both the reference to the browser AND the final result of the test!

package utils;

import java.lang.reflect.Field;
import java.lang.reflect.Method;
import org.junit.jupiter.api.extension.AfterTestExecutionCallback;
import org.junit.jupiter.api.extension.ExtensionContext;

public class ActionsOnFailureExtension implements AfterTestExecutionCallback {

    @Override
    public void afterTestExecution(ExtensionContext context) throws Exception {
        // if an ExecutionException is part of the context then the test failed
        Boolean testFailed = context.getExecutionException().isPresent();
        if (testFailed) {
            // take a screenshot via Java reflection
            try {
                Object clazz = context.getRequiredTestInstance();
                Method takeScreenshot = clazz.getClass().getMethod("takeScreenshot");
                // 'takeScreenshot' is a method in my test class
                // that uses the Selenium driver to take the screenshot
                // and then attaches it to the Allure report
                takeScreenshot.setAccessible(true);
                takeScreenshot.invoke(clazz);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }
}