When I try to run my simpletests, its running properly in browser at admin/config/development/testing. It shows complete results.

But when I run the same in command line as given below it gives empty results. I mean "Test summary" is empty and test runs in 0 sec. What might be the cause? 

root@mymachine:/var/www/html# php ./scripts/run-tests.sh --verbose --class BlogTestCase             

Drupal test run
---------------

Tests to be run:
 - Blog functionality (BlogTestCase)

Test run started:
 dinsdag, februari 6, 2018 - 15:32

Test summary
------------


Test run duration: 0 sec

Detailed test results
---------------------
root@mymachine:/var/www/html#