[GSoC] Add unit tests for `tune` API #1129

Job	Run time
e2e (v1.27.11, long-running-resume,from-volume-resume,median-stop)	14m 31s
e2e (v1.27.11, grid,bayesian-optimization,tpe,multivariate-tpe,cma-es,hyperband)	18m 26s
e2e (v1.27.11, file-metrics-collector,pytorchjob-mnist)	12m 49s
e2e (v1.27.11, median-stop-with-json-format,file-metrics-collector-with-json-format)	11m 41s
e2e (v1.28.7, long-running-resume,from-volume-resume,median-stop)	17m 6s
e2e (v1.28.7, grid,bayesian-optimization,tpe,multivariate-tpe,cma-es,hyperband)	20m 7s
e2e (v1.28.7, file-metrics-collector,pytorchjob-mnist)	13m 0s
e2e (v1.28.7, median-stop-with-json-format,file-metrics-collector-with-json-format)	11m 56s
e2e (v1.29.2, long-running-resume,from-volume-resume,median-stop)	16m 3s
e2e (v1.29.2, grid,bayesian-optimization,tpe,multivariate-tpe,cma-es,hyperband)	18m 47s
e2e (v1.29.2, file-metrics-collector,pytorchjob-mnist)	12m 21s
e2e (v1.29.2, median-stop-with-json-format,file-metrics-collector-with-json-format)	14m 2s
	3h 0m 49s

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