Fix testifylint & gci lint issues in apiserver/kubectl-plugin

[seanlaii]

Why are these changes needed?

After upgrading golangci-lint to v2 with the config in https://github.com/ray-project/kuberay/pull/4007/files, there are new lint issues for testifylint and gci:

$ golangci-lint run                   
experimental/cmd/main.go:15:1: File is not properly formatted (gci)

^
apiserver/pkg/model/converter_test.go:633:4: empty: use assert.Empty (testifylint)
                        assert.Equal(t, "", value.Name)
                        ^
apiserver/pkg/model/converter_test.go:648:2: empty: use assert.Empty (testifylint)
        assert.Equal(t, "", template.GpuAccelerator, "GPU accelerator mismatch")
        ^
apiserver/pkg/util/cluster_test.go:611:2: empty: use assert.Empty (testifylint)
        assert.Equal(t, "", configMap.Data["name"])
        ^
apiserver/pkg/util/cluster_test.go:612:2: empty: use assert.Empty (testifylint)
        assert.Equal(t, "", configMap.Data["namespace"])
        ^
apiserver/test/e2e/job_server_e2e_test.go:471:3: empty: use require.Empty (testifylint)
                require.Equal(t, "", continueToken) // Continue token should be empty because this is the last page
                ^
apiserver/test/e2e/job_server_e2e_test.go:485:3: empty: use require.Empty (testifylint)
                require.Equal(t, "", response.Continue) // Continue token should be empty because this is the last page
                ^
apiserver/test/e2e/job_server_e2e_test.go:496:3: empty: use require.Empty (testifylint)
                require.Equal(t, "", response.Continue) // Continue token should be empty because this is the last page
                ^
kubectl-plugin/pkg/cmd/get/get_cluster_test.go:332:4: len: use assert.Len (testifylint)
                        assert.Equal(t, len(tc.expectedRayClusters), len(rayClusters.Items))
                        ^
9 issues:
* gci: 1
* testifylint: 8

We address the issues for gci and testifylint in this PR.

Related issue number

Part of #4008

Checks

• I've made sure the tests are passing.
• Testing Strategy
  • Unit tests
  • Manual tests
  • This PR is not tested :(

[seanlaii]

/retest