if err != test.wErr {
				gotFitErr, gotOK := err.(*framework.FitError)
				wantFitErr, wantOK := test.wErr.(*framework.FitError)
				if gotOK != wantOK {
					t.Errorf("Expected err to be FitError: %v, but got %v (error: %v)", wantOK, gotOK, err)
				} else if gotOK {
					if diff := cmp.Diff(wantFitErr, gotFitErr); diff != "" {