TestNG tests not executed when @Test annotation is used for class

such behaviour is not compatible with what TestNG users can expect. See TestNG documentation:
http://testng.org/doc/documentation-main.html#class-level
"The effect of a class level @Test annotation is to make all the public methods of this class to become test methods even if they are not annotated. You can still repeat the @Test annotation on a method if you want to add certain attributes."

for example tests from this class will not be executed

import org.testng.annotations.Test;
import static org.testng.Assert.assertTrue;

@Test
public class MyClassTestNGTest {

public void testMyClass()

}

run "gradle test" on the attached project to see it happening (or rather not happening)