[WIP] Add unit test for `tune` api #1608

Job	Run time
Publish Image (earlystopping-medianstop, cmd/earlystopping/medianstop/v1beta1/Dockerfile) / Publish Image	3m 11s
Publish Image (suggestion-darts, cmd/suggestion/nas/darts/v1beta1/Dockerfile) / Publish Image	1m 10s
Publish Image (suggestion-enas, cmd/suggestion/nas/enas/v1beta1/Dockerfile) / Publish Image	5m 9s
Publish Image (suggestion-goptuna, cmd/suggestion/goptuna/v1beta1/Dockerfile) / Publish Image	5m 33s
Publish Image (suggestion-hyperband, cmd/suggestion/hyperband/v1beta1/Dockerfile) / Publish Image	3m 59s
Publish Image (suggestion-hyperopt, cmd/suggestion/hyperopt/v1beta1/Dockerfile) / Publish Image	3m 26s
Publish Image (suggestion-optuna, cmd/suggestion/optuna/v1beta1/Dockerfile) / Publish Image	1m 48s
Publish Image (suggestion-pbt, cmd/suggestion/pbt/v1beta1/Dockerfile) / Publish Image	1m 57s
Publish Image (suggestion-skopt, cmd/suggestion/skopt/v1beta1/Dockerfile) / Publish Image	3m 5s
	29m 18s

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