* tests: add abstract class for all database related tests
* tests: add abstract class for all ModelsCommand related tests
* tests: add GenerateBasicPhpdoc test
* tests: add CustomDate test
* tests: remove MITM abstract TestCaseDatabase, not useful here
* tests: skip new ModelsCommand test on Laravel < 6
* tests: remove CarbonImmutable checked
Since we decided to skip for Laravel < 6.0 anyway, it's always present
