Can't seem to connect to database

Thanks for this great project. I have tried to implement it faithfully, but three of the four tests fail. Most of the errors seem to be that they can't connect to the database.

PHPUnit 6.5.14 by Sebastian Bergmann and contributors. 46 Runtime: PHP 7.3.12 with Xdebug 2.9.0 47 Configuration: /builds/gettysburger/cbhsq8-ci/phpunit.xml.dist 48 Test 'Drupal\Tests\demo_module\Unit\DemoModuleExampleServiceTest::testConstruct' started 49 Test 'Drupal\Tests\demo_module\Unit\DemoModuleExampleServiceTest::testConstruct' ended 50 Test 'Drupal\Tests\demo_module\Unit\DemoModuleExampleServiceTest::testGetLastNode' started 51 Test 'Drupal\Tests\demo_module\Unit\DemoModuleExampleServiceTest::testGetLastNode' ended 52 Test 'Drupal\Tests\demo_module\Kernel\ExampleTest::testBlockRendering' started 53 Test 'Drupal\Tests\demo_module\Kernel\ExampleTest::testBlockRendering' ended 54 Time: 7.95 seconds, Memory: 12.00MB 55 There was 1 error: 56 1) Drupal\Tests\demo_module\Kernel\ExampleTest::testBlockRendering 57 PDOException: SQLSTATE[HY000] [2002] php_network_getaddresses: getaddrinfo failed: Name or service not known 58 /builds/gettysburger/cbhsq8-ci/web/core/lib/Drupal/Core/Database/Driver/mysql/Connection.php:420 59 /builds/gettysburger/cbhsq8-ci/web/core/lib/Drupal/Core/Database/Database.php:371 60 /builds/gettysburger/cbhsq8-ci/web/core/lib/Drupal/Core/Database/Database.php:166 61 /builds/gettysburger/cbhsq8-ci/web/core/tests/Drupal/KernelTests/KernelTestBase.php:354 62 /builds/gettysburger/cbhsq8-ci/web/core/tests/Drupal/KernelTests/KernelTestBase.php:235 63 /builds/gettysburger/cbhsq8-ci/web/modules/custom/demo_module/tests/src/Kernel/ExampleTest.php:24 64 Caused by 65 PDOException: PDO::__construct(): php_network_getaddresses: getaddrinfo failed: Name or service not known

I get these errors whether I point to your docker image in GitLab or my own custom image made with your Dokerfile. Thanks.

Best, Stephen Recker