I have a TestListener class, which implements ITestListener, which is responsible for taking pictures and saving the html if a selenium test fails.

My selenium tests have a parent class BaseTest, which helps do common tasks, like initiating each driver.

The content of each important area:

TestListener

public class TestListener implements ITestListener {
    WebDriver driver=null;
    ITestContext context = null;
    String filePath = "artifacts/";

    @Override
    public void onTestFailure(ITestResult result) {
        ITestContext context = result.getTestContext();
        driver = (WebDriver) context.getAttribute("WebDriver");
        System.out.println("***** Error "+result.getName()+" test has failed *****");
        String methodName=result.getName().toString().trim();
        String currentTime = getCurrentTime();
        saveScreenShot(methodName, currentTime);
        savePageSource(methodName, currentTime);
        saveConsoleLog(methodName, currentTime);
    }
...

BaseTest (each test calls this separately)

    private void testngSetup(ITestContext context){
        context.setAttribute("WebDriver", driver);
        TestRunner runner = (TestRunner) context;
        runner.setOutputDirectory(artifactLocation);
    }

pom.xml

        <plugin>
          <artifactId>maven-surefire-plugin</artifactId>
          <version>3.2.5</version>
          <configuration>
            <suiteXmlFiles>
              <suiteXmlFile>testng.xml</suiteXmlFile>
            </suiteXmlFiles>
            <useSystemClassLoader>false</useSystemClassLoader>
          </configuration>
        </plugin>

testng.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE suite SYSTEM "http://testng.org/testng-1.0.dtd">
<suite name="esm4hpc">
    <listeners>
        <listener class-name="selenium.listeners.TestListener"/>
    </listeners>
    <test name="sample-Test" verbose="2" parallel = "classes">
        <packages>
            <package name=".*"/>
        </packages>
    </test>
</suite>

I have found this thread (How to get the current class driver in ItestListener), which suggested to change getting the driver in ITestListener the following way: (WebDriver)result.getTestClass().getRealClass().getDeclaredField("driver").get(result.getInstance()), but it throw java.lang.NoSuchFieldException : driver

public class TestListener implements ITestListener {
    WebDriver driver=null;
    ITestContext context = null;
    String filePath = "artifacts/";

    @Override
    public void onTestFailure(ITestResult result) {
        ITestContext context = result.getTestContext();
        driver = (WebDriver)result.getTestClass().getRealClass().getDeclaredField("driver").get(result.getInstance());
        System.out.println("***** Error "+result.getName()+" test has failed *****");
        String methodName=result.getName().toString().trim();
        String currentTime = getCurrentTime();
        saveScreenShot(methodName, currentTime);
        savePageSource(methodName, currentTime);
        saveConsoleLog(methodName, currentTime);
    }
...

I have also tried to set the parallel tag in testng.xml to false, but did not seem to help.
I also tried to list each testing class separately, but it also gave back wrong pictures.

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE suite SYSTEM "http://testng.org/testng-1.0.dtd">
<suite name="esm4hpc">
    <listeners>
        <listener class-name="selenium.listeners.TestListener"/>
    </listeners>
    <test name="sample-Test" verbose="2" parallel = "false">
        <classes>
            <class name="selenium.esm4hpc.AuthenticationTest"/>
            <class name="selenium.esm4hpc.FileEditorTest"/>
            <class name="selenium.esm4hpc.FileManagerTest"/>
            <class name="selenium.esm4hpc.JobTest"/>
            <class name="selenium.esm4hpc.ProjectTest"/>
        </classes>
    </test>
</suite>

The only thing seemed to help is to move each test class into different test-cases:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE suite SYSTEM "http://testng.org/testng-1.0.dtd">
<suite name="esm4hpc">
    <listeners>
        <listener class-name="selenium.listeners.TestListener"/>
    </listeners>
    <test name="AuthenticationTest" verbose="2" parallel = "false">
        <classes>
            <class name="selenium.esm4hpc.AuthenticationTest"/>
        </classes>
    </test>
    <test name="FileEditorTest" verbose="2" parallel = "false">
        <classes>
            <class name="selenium.esm4hpc.FileEditorTest"/>
        </classes>
    </test>
    <test name="FileManagerTest" verbose="2" parallel = "false">
        <classes>
            <class name="selenium.esm4hpc.FileManagerTest"/>
        </classes>
    </test>
    <test name="JobTest" verbose="2" parallel = "false">
        <classes>
            <class name="selenium.esm4hpc.JobTest"/>
        </classes>
    </test>
    <test name="ProjectTest" verbose="2" parallel = "false">
        <classes>
            <class name="selenium.esm4hpc.ProjectTest"/>
        </classes>
    </test>
</suite>

But this causes the result files to be generated separately, which makes it cumbersome to debug failed cases.