Drupal8 Testing "Log in" not found

When I run the drupal run-test.sh, I get the following error.

Behat\Mink\Exception\ElementNotFoundException: Button with
 id|name|label|value "Log in" not found.

If you look at the results of the execution, GET request to: http://localhost:8888/drupal8/user/login is redirected to redirecting to /drupal8/core/install.php and the " The "Log in" button seems to be missing. How do I solve this problem?