Oauth failures in pkg/storage/chunk/gcp Test_Hedging

[bboreham]

Describe the bug
When I tried to run Loki unit tests locally I got errors like this:

--- FAIL: Test_Hedging (1.02s)
    --- FAIL: Test_Hedging/delete/put/list_are_not_hedged (0.38s)
        gcs_object_client_test.go:77: 
                Error Trace:    gcs_object_client_test.go:77
                Error:          Not equal: 
                                expected: 3
                                actual  : 0

Much single-stepping identified that the call was failing on an Oauth token fetch to http://oauth2.googleapis.com/.

Removing ~/.config/gcloud/application_default_credentials.json gave a simpler error:

--- FAIL: Test_Hedging (0.62s)
    --- FAIL: Test_Hedging/delete/put/list_are_not_hedged (0.22s)
        gcs_object_client_test.go:75: 
                Error Trace:    gcs_object_client_test.go:75
                Error:          Received unexpected error:
                                google: could not find default credentials. See https://developers.google.com/accounts/docs/application-default-credentials for more information.

I submit that this unit test should not be contacting Google for Oauth tokens.

To Reproduce

$ mv ~/.config/gcloud/application_default_credentials.json /tmp/
$ go test github.com/grafana/loki/pkg/storage/chunk/gcp

Expected behavior
Tests pass without contacting Google.

Environment:

Linux vagrant 5.4.0-72-generic #80-Ubuntu SMP Mon Apr 12 17:35:00 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux