The export happens in a reducer, whois instance fields all need to be serializable. The DriveConnection is therefore installed as a class variable that can be replaced with a mock during test. Class variables are not serialized. Only fields related to a particular instance are.
Note that DriveConnection is a misnomer. It is not a connection at all. It is just a thin wrapper class around the Drive service class, which provides convenient methods to write into Drive. Regardless, it cannot be serialized.
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Created by MOE: https://github.com/google/moe
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ebce333d5b