[GSoC] Add unit tests for `tune` API #1835

Job	Run time
Publish Image (earlystopping-medianstop, cmd/earlystopping/medianstop/v1beta1/Dockerfile) / Publish Image	3m 9s
Publish Image (suggestion-darts, cmd/suggestion/nas/darts/v1beta1/Dockerfile) / Publish Image	1m 23s
Publish Image (suggestion-enas, cmd/suggestion/nas/enas/v1beta1/Dockerfile) / Publish Image	4m 55s
Publish Image (suggestion-goptuna, cmd/suggestion/goptuna/v1beta1/Dockerfile) / Publish Image	5m 31s
Publish Image (suggestion-hyperband, cmd/suggestion/hyperband/v1beta1/Dockerfile) / Publish Image	3m 44s
Publish Image (suggestion-hyperopt, cmd/suggestion/hyperopt/v1beta1/Dockerfile) / Publish Image	2m 48s
Publish Image (suggestion-optuna, cmd/suggestion/optuna/v1beta1/Dockerfile) / Publish Image	1m 42s
Publish Image (suggestion-pbt, cmd/suggestion/pbt/v1beta1/Dockerfile) / Publish Image	2m 40s
Publish Image (suggestion-skopt, cmd/suggestion/skopt/v1beta1/Dockerfile) / Publish Image	2m 40s
	28m 32s

Provide feedback