[UnitTest] Add another unit tests to the data structures that contain the metadata.
[UnitTest] Add another unit tests to the data structures that contain the metadata.

I am adding this test mainly to check that the code that removed the sentinal
value and replaced it with a nullable pointer and some logic for initializing
the pointer works.

khizkhiz/swift,khizkhiz/swift,khizkhiz/swift,khizkhiz/swift,khizkhiz/swift,khizkhiz/swift,khizkhiz/swift