tests: Migrate all tests to Feature and suite based

[Xuanwo]

Background

For now, our tests are using convey to write BDD test. However, they could be much simpler if we write them using github.com/stretchr/testify/suite.

Here is an example: #1020

[Joey2132]

So, actually before I handle issue 975, this issue has to be finished first. Is anyone doing it now? If not, I'd like to do it.

[Xuanwo]

The issue is free for you to take! However, I think it's better to finish #975 before take on this issue.

[Joey2132]

The issue is free for you to take! However, I think it's better to finish #975 before take on this issue.

OK, I will finish #975 first.