ALL: Investigate improving unit testing around low level native calls

There are a few empty unit test cases that have yet to be implemented in Java and C# (`LibcProtectedMemoryAllocatorTest` in particular). The affected library source code is covered via other unit tests that are in place, but some of the low level native calls are difficult to unit test in the traditional sense. We could theoretically setup functional/integration tests to cover them.

Locate the empty Java and C# unit tests, especially LibcProtectedMemoryAllocatorTest, and read the existing tests covering the affected library source. Determine whether the low-level native calls can be covered with unit tests or require functional/integration tests; done means the testing approach is decided and the relevant coverage is implemented.

Written by the indexing model from the issue text.