org.testng.TestNGException: while trying to execute the tests

Discussion and help from @juherr suggests that solution to this is :

Attribute "parallel" with value "none" must have a value from the list "false methods tests classes instances ".

TestNG 6.9.10 is now validating the xml file against the DTD The problem is that the default testng.xml template from IntelliJ is setting "parallel" on suite to "none". Here is the link to the bug for the same.

update the testng.xml to

<suite name="Suite" parallel="false">

from

<suite name="Suite" parallel="none">