Not all unit tests are here, many are also embedded as inner classes of the main code (such as here: rxjava-core/src/main/java/rx/operators).

• For an explanation of this design choice see Ben J. Christensen's JUnit Tests as Inner Classes.

Also, each of the language adaptors has a /src/test/ folder which further testing (see Groovy for an example: language-adaptors/rxjava-groovy/src/test).