Added ExplainAdminCommandTest

BC Break: some methods from Admin class are added to AdminInterface (needed to implement the tests properly).

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | yes
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | n/a
| License       | MIT
| Doc PR        | n/a