The unit tests run locally against an example fake and do not require any configuration.
go test --short
The integration tests will reach out and store, read and then delete a value from a datastore. You have to provide the DATASTORE_PROJECT_ID environment variable and the client has to be able to find credentials.
For example:
DATASTORE_PROJECT_ID=<proj-id> GOOGLE_APPLICATION_CREDENTIALS=</path/to/creds.json> go test