When I used Mysql and MongoDB as my database at the same time, there was something wrong with using TestCase.

[Zhipeng Guan]

I use MySQL as my default database, and I just used this database in unit tests.

But he used all my database connections while executing the "connections_support_transactions" function.

This caused all my data in MySQL initialization to be clear.

I modified the code of TestCase to this way.

https://gist.github.com/elfgzp/4b74a4b0860f3cecba17c56979e8e116

I want to know if this is a bug.