migrate test-infra to testify for util/admin pkg

[tisonkun]

No description provided.

[evilbinary]

Hi @tisonkun, I'd like to migrate tests under util/admin pkg. Please create a subtask and assign to me.

[tisonkun]

/assign @evilbinary

Glad to see your interest @evilbinary ! That is the subtask and I will assign it to you.

[jyz0309]

Hello~ @evilbinary
I notice that the admin_integration_test.go have used a lot of testKit.MustExec(). And we have not implemented another testkit yet. So I think you can migrate test-infra to testify for admin_test.go first.
What do you think? @tisonkun

[tisonkun]

Yep. That makes sense. Besides, we shall make the first migration of testkit.TestKit example asap :P