Revisiting tests to have reusable mocks

[gauravgahlot]

Description

The PR restructures mocking based on the suggestion by @gianarb in this thread.

Why is this needed

To write more flexible and|or reusable mocks.

How Has This Been Tested?

The changes include unit tests only.

Coverage

➜ go test -coverprofile coverage.out
➜ go tool cover -func coverage.out | grep tinkerbell.go
github.com/tinkerbell/tink/grpc-server/tinkerbell.go:29:	GetWorkflowContexts	0.0%
github.com/tinkerbell/tink/grpc-server/tinkerbell.go:49:	GetWorkflowContextList	100.0%
github.com/tinkerbell/tink/grpc-server/tinkerbell.go:72:	GetWorkflowActions	100.0%
github.com/tinkerbell/tink/grpc-server/tinkerbell.go:81:	ReportActionStatus	100.0%
github.com/tinkerbell/tink/grpc-server/tinkerbell.go:138:	UpdateWorkflowData	100.0%
github.com/tinkerbell/tink/grpc-server/tinkerbell.go:155:	GetWorkflowData		100.0%
github.com/tinkerbell/tink/grpc-server/tinkerbell.go:168:	GetWorkflowMetadata	100.0%
github.com/tinkerbell/tink/grpc-server/tinkerbell.go:177:	GetWorkflowDataVersion	100.0%
github.com/tinkerbell/tink/grpc-server/tinkerbell.go:185:	getWorkflowsForWorker	100.0%
github.com/tinkerbell/tink/grpc-server/tinkerbell.go:196:	getWorkflowActions	100.0%
github.com/tinkerbell/tink/grpc-server/tinkerbell.go:206:	isApplicableToSend	100.0%
github.com/tinkerbell/tink/grpc-server/tinkerbell.go:233:	isLastAction		100.0%

How are existing users impacted? What migration steps/scripts do we need?

No impact.

Checklist:

I have:

• updated the documentation and/or roadmap (if required)
• added unit or e2e tests
• provided instructions on how to upgrade

[gianarb]

Yep! That's the right direciton!! Thank you for doing it @gauravgahlot

[gianarb]

Can you squash your commits please?

[codecov]

Codecov Report

Merging #256 into master will increase coverage by 1.45%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #256      +/-   ##
==========================================
+ Coverage   10.90%   12.36%   +1.45%     
==========================================
  Files           7        7              
  Lines        1165     1165              
==========================================
+ Hits          127      144      +17     
+ Misses       1019     1010       -9     
+ Partials       19       11       -8     

Impacted Files	Coverage Δ
grpc-server/tinkerbell.go	90.83% <0.00%> (+12.97%)	⬆️

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