public class RunJUnit5TestsFromJava {
SummaryGeneratingListener listener = new SummaryGeneratingListener();

public void runOne() {
    LauncherDiscoveryRequest request = LauncherDiscoveryRequestBuilder.request()
      .selectors(selectClass(FirstUnitTest.class))
      .build();
    Launcher launcher = LauncherFactory.create();
    TestPlan testPlan = launcher.discover(request);
    launcher.registerTestExecutionListeners(listener);
    launcher.execute(request);
}

// main method...
public static void main(String[] args) {
RunJUnit5TestsFromJava runner = new RunJUnit5TestsFromJava();
runner.runAll();

TestExecutionSummary summary = runner.listener.getSummary();
summary.printTo(new PrintWriter(System.out));
}

public void runAll() {
LauncherDiscoveryRequest request = LauncherDiscoveryRequestBuilder.request()
  .selectors(selectPackage("com.baeldung.junit5.runfromjava"))
  .filters(includeClassNamePatterns(".*Test"))
  .build();
Launcher launcher = LauncherFactory.create();
TestPlan testPlan = launcher.discover(request);
launcher.registerTestExecutionListeners(listener);
launcher.execute(request);
}

}

how to use this to get an out put from a existing java file to test it

public class RunJUnit5TestsFromJava {
SummaryGeneratingListener listener = new SummaryGeneratingListener();

public void runOne() {
    LauncherDiscoveryRequest request = LauncherDiscoveryRequestBuilder.request()
      .selectors(selectClass(FirstUnitTest.class))
      .build();
    Launcher launcher = LauncherFactory.create();
    TestPlan testPlan = launcher.discover(request);
    launcher.registerTestExecutionListeners(listener);
    launcher.execute(request);
}

// main method...
public static void main(String[] args) {
RunJUnit5TestsFromJava runner = new RunJUnit5TestsFromJava();
runner.runAll();

TestExecutionSummary summary = runner.listener.getSummary();
summary.printTo(new PrintWriter(System.out));
}

public void runAll() {
LauncherDiscoveryRequest request = LauncherDiscoveryRequestBuilder.request()
  .selectors(selectPackage("com.baeldung.junit5.runfromjava"))
  .filters(includeClassNamePatterns(".*Test"))
  .build();
Launcher launcher = LauncherFactory.create();
TestPlan testPlan = launcher.discover(request);
launcher.registerTestExecutionListeners(listener);
launcher.execute(request);
}

}