How can I do unit test when I use router flex in my code.

### Version
Tell us which versions you are using:

- react-native-router-flux v4.?.? (v3 is not supported)
- react-native v0.?.?

### Expected behaviour
I don't find unit test example.

### Actual behaviour
How can I do unit test when I use router flex in my code.

### Steps to reproduce
For non-obvious bugs, please fork this component, modify Example project to reproduce your issue and include link here.
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