pkg/docker/config: Bring auth tests from docker/docker_client_test

[wking]

Shifted a number of auth-getting unit tests from docker_client_test.go into config_test.go, since they only excercise config.go logic. They'd been in their previous location since landing in d30079f (#96).

Spun off from #588.

[wking]

GitHub doesn't do a great job of showing these moves, but this is basically a giant copy/paste with some config.GetAuthentication -> GetAuthentication changes.

$ git describe
v1.3-49-gd8920c2
$ git blame -C pkg/docker/config/config_test.go | grep Trevor
d8920c26 pkg/docker/config/config_test.go (W. Trevor King  2019-02-25 14:29:56 -0800   4) 	"encoding/base64"
d8920c26 pkg/docker/config/config_test.go (W. Trevor King  2019-02-25 14:29:56 -0800   5) 	"encoding/json"
d8920c26 pkg/docker/config/config_test.go (W. Trevor King  2019-02-25 14:29:56 -0800   9) 	"path/filepath"
d8920c26 pkg/docker/config/config_test.go (W. Trevor King  2019-02-25 14:29:56 -0800  10) 	"reflect"
d8920c26 pkg/docker/config/config_test.go (W. Trevor King  2019-02-25 14:29:56 -0800  14) 	"github.com/containers/storage/pkg/homedir"
d8920c26 pkg/docker/config/config_test.go (W. Trevor King  2019-02-25 14:29:56 -0800  15) 	"github.com/pkg/errors"
d8920c26 pkg/docker/config/config_test.go (W. Trevor King  2019-02-25 14:29:56 -0800 236) 			username, password, err := GetAuthentication(sys, tc.hostname)
d8920c26 pkg/docker/config/config_test.go (W. Trevor King  2019-02-25 14:29:56 -0800 319) 		username, password, err := GetAuthentication(nil, tc.hostname)
d8920c26 pkg/docker/config/config_test.go (W. Trevor King  2019-02-25 14:29:56 -0800 390) 	username, password, err := GetAuthentication(nil, "index.docker.io")
d8920c26 pkg/docker/config/config_test.go (W. Trevor King  2019-02-25 14:29:56 -0800 443) 	username, password, err := GetAuthentication(nil, "index.docker.io")
d8920c26 pkg/docker/config/config_test.go (W. Trevor King  2019-02-25 14:29:56 -0800 454) 	username, password, err = GetAuthentication(nil, "index.docker.io")
d8920c26 pkg/docker/config/config_test.go (W. Trevor King  2019-02-25 14:29:56 -0800 465) 	username, password, err = GetAuthentication(nil, "index.docker.io")
d8920c26 pkg/docker/config/config_test.go (W. Trevor King  2019-02-25 14:29:56 -0800 477) 	username, password, err = GetAuthentication(nil, "index.docker.io")
d8920c26 pkg/docker/config/config_test.go (W. Trevor King  2019-02-25 14:29:56 -0800 484) }
d8920c26 pkg/docker/config/config_test.go (W. Trevor King  2019-02-25 14:29:56 -0800 485) 

[wking]

I could simplify further by dropping the test-only types (e.g. testAuthConfigEntry is the same as dockerAuthConfig). I haven't done that yet to keep the change easy to review, but I can do it in this commit, or in a separate commit in this PR, or in a follow-up PR. Just let me know if/what you want :).

[wking]

Rebased onto master with 79cc881 -> 5299d35 to address GitHub's "This branch is out-of-date with the base branch" message.

[mtrmac]

LGTM. Thanks!

I could simplify further by dropping the test-only types (e.g. testAuthConfigEntry is the same as dockerAuthConfig).

That would defeat the point of testing that the file decoding works as expected, and that the decoded types were not changed without anyone noticing. Ideally we should have hard-coded fixtures in the repo instead of creating the configs at runtime.

[wking]

Ideally we should have hard-coded fixtures in the repo...

Filed with #593 ;)