You have seen how to use the Kotlin collection API in great detail. You have learned how the standard library provides you with the distinction between immutable and mutable collection types, and how immutability is achieved at the interface level. You know now that Kotlin doesn't add any new collection, but rather relies on the existing Java large-collection library. Type aliasing done by the Kotlin compiler is not a mystery anymore. Now you can go and use the arrays properly because you leaned to use the specific implementations over the generic one when it comes to primitive types.

The Kotlin standard library provides you with the building blocks to express complex computations via a few simple extension methods, hopefully giving you a different perspective when it comes to choosing your next project language.

This chapter covers unit and integration testing using Kotlin using unit test frameworks. Unit testing is often a gateway into a new language, and this is no different.