storage/spanner.go could use some tests.

[bgood]

This file could really use some test cases. This is where most of the important stuff is happening; The translation from DynamoDB to Spanner and back. Having test cases for it automatically also means that we have a sort of documentation of what is supported and what is not.

Originally posted by @olavloite in #3 (comment)

[iyertalks]

Please assign to me.