[GSoC] Add unit tests for `tune` API #1997

Job	Run time
Publish Image (darts-cnn-cifar10-cpu, linux/amd64,linux/arm64, examples/v1beta1/trial-images/dart... / Publish Image	18m 34s
Publish Image (enas-cnn-cifar10-cpu, linux/amd64,linux/arm64, examples/v1beta1/trial-images/enas-... / Publish Image	18m 42s
Publish Image (darts-cnn-cifar10-gpu, linux/amd64, examples/v1beta1/trial-images/darts-cnn-cifar1... / Publish Image	20m 3s
Publish Image (enas-cnn-cifar10-gpu, linux/amd64, examples/v1beta1/trial-images/enas-cnn-cifar10/... / Publish Image	13m 6s
Publish Image (pytorch-mnist-cpu, linux/amd64,linux/arm64, examples/v1beta1/trial-images/pytorch-... / Publish Image	17m 14s
Publish Image (pytorch-mnist-gpu, linux/amd64, examples/v1beta1/trial-images/pytorch-mnist/Docker... / Publish Image	6m 21s
Publish Image (simple-pbt, linux/amd64,linux/arm64, examples/v1beta1/trial-images/simple-pbt/Dock... / Publish Image	11m 21s
Publish Image (tf-mnist-with-summaries, linux/amd64,linux/arm64, examples/v1beta1/trial-images/tf... / Publish Image	18m 36s
	2h 3m 57s

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