If you have already included the fragment below in your web.xml, this is most probably about jar dependency.
<servlet>
<servlet-name>ArquillianServletRunner</servlet-name>
<servlet-class>org.jboss.arquillian.protocol.servlet.runner.ServletTestRunner</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>ArquillianServletRunner</servlet-name>
<url-pattern>/ArquillianServletRunner</url-pattern>
</servlet-mapping>
First, you can check if ArquillianServlet running sending a GET request like below
http://localhost:8080/APP_CONTEXT_ROOT/ArquillianServletRunner?outputMode=serializedObject&className=com.stackoverflow.test.SampleTest&methodName=testSomething
Besides, you can also have a look inside server log and you can see NoClassDefFoundError. Fix your dependencies, then try again.