Add more test cases for SimpleAliasRegistry to increase coverage test.

Comment From: pivotal-cla

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Comment From: pivotal-cla

@nhavuong Thank you for signing the Contributor License Agreement!

Comment From: sbrannen

This has been merged into main in 345d8186d4a2153e20a2e13c21ea8686987a0031 and slightly revised in 432fdad7d06ff3de4d61cdb3003f728525473d69.

I also added you as an @author in SimpleAliasRegistryTests. If you would like me to remove that, just let me know.

Thanks for your contribution!