text: Title: Replace reflect.DeepEqual with cmp.Diff in tests
  Body: /kind feature
  
  **Describe the solution you'd like**
  [A clear and concise description of what you want to happen.]
  To improve visibility, we should replace `reflect.DeepEqual` with `cmp.Diff` in all test cases: https://github.com/kubeflow/katib/blob/master/docs/developer-guide.md#go-development
  
  Here is an example for using `cmp.Diff`: https://github.com/kubeflow/katib/blob/8df3c5c8383db6ee601f0ed8642cd554ee2234b6/pkg/apis/config/v1beta1/defaults_test.go#L88-L90
  
  **Anything else you would like to add:**
  [Miscellaneous information that will assist in solving the issue.]
  
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