<suite name="suite1" configfailurepolicy="continue" parallel="classes">
  <test name="test1">
    <classes>
      <class name="class1"/>
      <class name="class2"/>
      <class name="class3"/>
    </classes>
  </test>
</suite>

Thread1 - class1.a();
Thread1 – class2.a();
Thread2 – class3.a();
Thread2 – class1.b();
Thread1 – class3.a;
…

<suite name="suite1" configfailurepolicy="continue" parallel="tests">
  <test name="test1">
    <classes>
      <class name="class1"/>
    </classes>
  </test>
  <test name="test2">
    <classes>
      <class name="class2"/>
    </classes>
  </test>
  <test name="test3">
    <classes>
      <class name="class3"/>
    </classes>
  </test>
</suite>

Thread1 - class1.a();
Thread1 – class1.b();
Thread1 – class1.c();
Thread2 – class2.a();
Thread2 – class2.b();
Thread1 – class3.a();