Testing

public class CoolFeatureTest {
  @Test void someTest() {
    // …
  }

  @Test void someOtherTest() {
    // …
  }
}

@Rule public JenkinsRule j = new JenkinsRule();

@Test public void someTest() {
  EnvironmentVariablesNodeProperty prop = new EnvironmentVariablesNodeProperty();
  EnvVars env = prop.getEnvVars();
  env.put("DEPLOY_TARGET", "staging");
  j.jenkins.getGlobalNodeProperties().add(prop);
  // …
}

import org.jenkinsci.plugins.workflow.job.WorkflowJob;
import org.junit.Test;
import org.jvnet.hudson.test.JenkinsRule;
import org.jvnet.hudson.test.recipes.LocalData;

import hudson.model.Computer;
import hudson.model.FreeStyleProject;
import hudson.model.labels.LabelAtom;
import hudson.slaves.DumbSlave;
import hudson.slaves.JNLPLauncher;

public class WithAgentTest {

  @Rule
  public JenkinsRule jenkinsRule = new JenkinsRule();

  @Test
  @LocalData // Suppose you have already created a Freestyle and a WorkflowJob
  public void test_agent() throws Exception {
    // Creating the agent with a specific label
    LabelAtom testingLabel = new LabelAtom("testing");
    DumbSlave agent = jenkinsRule.createSlave(testingLabel);
    /* If you need to change the Launcher
    agent.setLauncher(new JNLPLauncher(true));
    agent.save();
    */
    // Connecting the agent
    jenkinsRule.waitOnline(agent);
    /*
    Alternative to waitOnline would be to use the Computer object, but you must check the agent becomes
    online. Better use waitOnline

    Computer computer = agent.toComputer();
    while (!computer.isOnline()) {
      computer.connect(true);
    }
    */

    FreeStyleProject freeStyleProject = jenkinsRule.jenkins.getItemByFullName("my-freestyle", FreeStyleProject.class);
    freeStyleProject.setAssignedLabel(testingLabel);
    // Testing the job

    WorkflowJob workflowJob = jenkinsRule.jenkins.getItemByFullName("my-workflow", WorkflowJob.class);
    // Testing the job
  }
}

pipeline {
  agent {
    label 'testing'
  }

  stages {
    stage('Hello') {
      steps {
        sh 'echo Hello world'
      }
    }
  }
}

computer.disconnect(new OfflineCause.IdleOfflineCause());

import com.gargoylesoftware.htmlunit.FailingHttpStatusCodeException;

import org.junit.Assert;
import org.junit.Rule;
import org.junit.Test;

import org.jvnet.hudson.test.JenkinsRule;
import org.jvnet.hudson.test.MockAuthorizationStrategy;

public class MyTest {

  @Rule
  public JenkinsRule j = new JenkinsRule();

  @Test
  public void testAccess() throws Exception {
    // create a dummy security realm
    j.jenkins.setSecurityRealm(j.createDummySecurityRealm());
    // setup a MockAuthorizationStrategy
    MockAuthorizationStrategy authorizationStrategy = new MockAuthorizationStrategy();
    authorizationStrategy.grant(Jenkins.READ).onRoot().toEveryone();
    authorizationStrategy.grant(Item.DISCOVER).everywhere().to("alice");
    authorizationStrategy.grant(Item.READ).everywhere().to("bob");
    j.jenkins.setAuthorizationStrategy(authorizationStrategy);

    // create a freestyle project for test
    j.createFreeStyleProject("myproject");

    // alice can discover project
    JenkinsRule.WebClient alice = j.createWebClient().login("alice");
    FailingHttpStatusCodeException e = assertThrows(FailingHttpStatusCodeException.class, () -> alice.goTo("bypass/myproject"));
    Assert.assertEquals("alice can discover", 403, e.getStatusCode());

    // bob can read project
    JenkinsRule.WebClient bob = j.createWebClient().login("bob");
    bob.goTo("bypass/myproject"); // success
  }

import java.util.logging.Level;
import org.junit.Rule;
import org.junit.Test;
import org.jvnet.hudson.test.LoggerRule;

import static org.hamcrest.Matchers.containsString;
import static org.junit.Assert.assertThat;
import static org.jvnet.hudson.test.LoggerRule.recorded;

public class MyTest {

  public @Rule LoggerRule l = new LoggerRule();

  @Test
  public void testLogs() throws Exception {
    l.capture(3).record("my.logger.name", Level.ALL);
    doThingThatLogs();
    assertThat(l, recorded(Level.INFO, containsString("Thing started successfully")));
  }
}