Material-ui: [Snapshot testing] className mismatch depending on all or single test run

[01e9]

• [X] I have searched the issues of this repository and believe that this is not a duplicate.

Update: It's reverse, with all tests run the class is MuiSelect-root-146 and with one test run it's MuiSelect-root-121.

Are you familiar with such case? What do you recommend to prevent this?

Steps to Reproduce (for bugs)

At the moment it's just a question. If it will become too annoying I will create a sandbox.

Your Environment

| Tech | Version |
|--------------|---------|
| Material-UI | 1.0.0-beta.45 |
| React | 16.3.2 |

[oliviertassinari]

@arteniioleg It's a duplicate of #9492. If the issue isn't enough, we can think of adding a guide in the docs. Let me know.

[01e9]

Add in docs please. In the issue there are many code examples, I would like the recommended one.