The purpose of this module is to test the snapshot mechanism by running the testsuite against a number of different providers to create a Codebase and then take a snapshot of the Codebase and perform the actual test against the snapshot. This will ensure that the snapshot provides the same capabilities as the original providers.
It does that by registering a com.android.tools.metalava.model.testing.transformer.CodebaseTransformer service which is loaded by the com.android.tools.metalava.model.testsuite.ModelSuiteRunner and used to transform the Codebase before performing the test.