When creating a Java library module in Android Studio it creates a default class under:
[module]
+ src/main/java/[com/foo/bar]
If you look into [module].iml file, you will find that path as well as the path for tests, that you can utilize. The below is a summary:
What you can do in particular is to create a directory for tests to have the following structure:
[module]
+ src/main/java/[com/foo/bar]
+ src/test/java/[com/foo/bar]
The above structure will be recognized by Android Studio and your files underneath will be included into the module.
I assume that that structure is a recommended layout for code and tests.
