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kotlinlang

as a general annotation processing question: how can i write unit tests for one? I can check the compilation output with the `kotlin-compile-testing`  library, but I’m interested in testing the functionality. Is the best option to create a new module which depends on the annotation processor and run tests there?

This is what we use in room for most of unit tests 
<https://cs.android.com/androidx/platform/frameworks/support/+/androidx-main:room/room-compiler-processing-testing/src/main/java/androidx/room/compiler/processing/util/ProcessorTestExt.kt;l=121|https://cs.android.com/androidx/platform/frameworks/support/+/androidx-main:room/room-compiler-processing-testing/src/main/java/androidx/room/compiler/processing/util/ProcessorTestExt.kt;l=121>

And for functionality, we use actual integration test apps
<https://cs.android.com/androidx/platform/frameworks/support/+/androidx-main:room/integration-tests/|https://cs.android.com/androidx/platform/frameworks/support/+/androidx-main:room/integration-tests/>

Btw, there are a lot more unit tests than integration tests  because you can create whatever broken case you want in unit tests vs integration tests can only test happy paths (and in my experience, writing a processor is a lot more about detecting developer errors :man-shrugging:)

do you have an example file with some of the unit tests?

Pretty much all tests in room compiler or x processing are unit tests.
E.g this is the test for pojos:
<https://cs.android.com/androidx/platform/frameworks/support/+/androidx-main:room/room-compiler/src/test/kotlin/androidx/room/processor/PojoProcessorTest.kt|https://cs.android.com/androidx/platform/frameworks/support/+/androidx-main:room/room-compiler/src/test/kotlin/androidx/room/processor/PojoProcessorTest.kt>

There is a lot of abstraction it ceremony in these tests so they might be harder to read for an unfamiliar person

These might be easier:
<https://cs.android.com/androidx/platform/frameworks/support/+/androidx-main:room/room-compiler-processing/src/test/java/androidx/room/compiler/processing/XArrayTypeTest.kt|https://cs.android.com/androidx/platform/frameworks/support/+/androidx-main:room/room-compiler-processing/src/test/java/androidx/room/compiler/processing/XArrayTypeTest.kt>

These are the tests for the abstraction between ksp javaap