[GSoC] Add unit tests for `tune` API #1249

Job	Run time
e2e (v1.29.2, long-running-resume,from-volume-resume,median-stop)	2m 11s
e2e (v1.29.2, grid,bayesian-optimization,tpe,multivariate-tpe,cma-es,hyperband)	2m 12s
e2e (v1.29.2, file-metrics-collector,pytorchjob-mnist)	2m 26s
e2e (v1.29.2, median-stop-with-json-format,file-metrics-collector-with-json-format)	2m 11s
e2e (v1.30.7, long-running-resume,from-volume-resume,median-stop)	2m 25s
e2e (v1.30.7, grid,bayesian-optimization,tpe,multivariate-tpe,cma-es,hyperband)	2m 24s
e2e (v1.30.7, file-metrics-collector,pytorchjob-mnist)	2m 24s
e2e (v1.30.7, median-stop-with-json-format,file-metrics-collector-with-json-format)	2m 24s
e2e (v1.31.3, long-running-resume,from-volume-resume,median-stop)	2m 24s
e2e (v1.31.3, grid,bayesian-optimization,tpe,multivariate-tpe,cma-es,hyperband)	2m 11s
e2e (v1.31.3, file-metrics-collector,pytorchjob-mnist)	2m 23s
e2e (v1.31.3, median-stop-with-json-format,file-metrics-collector-with-json-format)	2m 24s
	27m 59s

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