Story (Required)

As a developer using image-updater, I want to make sure all packages and commands are fully tested.  We should add tests to verify their expected behavior.

Describe the bug
According to the test coverage report at https://app.codecov.io/gh/argoproj-labs/argocd-image-updater/blob/master/pkg%2Fregistry%2Fclient.go , some important code paths are not covered in function:

func (client *registryClient) TagMetadata(manifest distribution.Manifest, opts *options.ManifestOptions) (*tag.TagInfo, error) {

Need to add tests for those code paths in https://github.com/argoproj-labs/argocd-image-updater/blob/master/pkg/registry/client.go#L198

Acceptance Criteria (Mandatory)

• analyze the current unit test coverage in pkg/registry/client.go
• add unit tests so that all testable code paths are covered
• code blocks that are not testable by unit tests under the current testing framework can be exempted
   

INVEST Checklist

Dependencies identified

Blockers noted and expected delivery timelines set

Design is implementable

Acceptance criteria agreed upon

Story estimated

Legend

Unknown

Verified

Unsatisfied

Done Checklist

• Code is completed, reviewed, documented and checked in
• Unit and integration test automation have been delivered and running cleanly in continuous integration/staging/canary environment
• Continuous Delivery pipeline(s) is able to proceed with new code included
• Customer facing documentation, API docs etc. are produced/updated, reviewed and published
• Acceptance criteria are met