kubelet: add unit tests for imagePullSecrets keyring

[andrewsykim]

Signed-off-by: Andrew Sy Kim kim.andrewsy@gmail.com

What type of PR is this?
/kind cleanup

What this PR does / why we need it:
Add unit tests for generating kubelet's docker keyring for imagePullSecrets.

Which issue(s) this PR fixes:

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

NONE

Additional documentation e.g., KEPs (Kubernetes Enhancement Proposals), usage docs, etc.:

[andrewsykim]

/assign @derekwaynecarr @dchen1107 @liggitt
/sig node

[liggitt]

what happens with default keyring and DockerConfigJsonKey or DockerConfigKey that doesn't match the given image?

[andrewsykim]

In this test case specifically, the default keyring would always return auth configs since the fake Lookup() call returns hardcoded auth configs. If we used a real keyring it would not return any auth configs if the image didn't match based on the check here:

kubernetes/pkg/credentialprovider/keyring.go

Lines 241 to 245 in 442a69c

	// both k and image are schemeless URLs because even though schemes are allowed
	// in the credential configurations, we remove them in Add.
	if matched, _ := urlsMatchStr(k, image); matched {
	ret = append(ret, dk.creds[k]...)
	}

[liggitt]

I was mostly looking for a test that exercised whether we fell back to the default or not for a DockerConfigJsonKey or DockerConfigKey that doesn't match the given image

[andrewsykim]

Ah, good point. Updated to include tests that only return credentials from the default keyring if DockerConfigJsonKey or DockerConfigKey didn't have a matching image URL passed into Lookup.

[liggitt]

/lgtm
/approve

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