how to exclude PHPUnit based functional tests from runnning? I am trying to run only unit test for my custom module. 

./vendor/bin/phpunit -c ./web/core ./web/modules/custom/testing_example --testsuite=unit .
But I keep getting the following error:    

There were 2 errors:

1) Drupal\Tests\testing_example\Kernel\ExampleFixtureManagementTest::testNodeCreation
Exception: There is no database connection so no tests can be run. You must provide a SIMPLETEST_DB environment variable to run PHPUnit based functional tests outside of run-tests.sh. See https://www.drupal.org/node/2116263#skipped-tests for more information.


I only want to run PhpUnit tests and not functional/browser tests.
Since those tests are grouped by namespace/directory, you can just pass the respective path to phpunit, simply add tests/src/Unit to your existing path.