How to write simple tests for client-go using a fake client?

Question

Problem

I am looking for the correct way to test my code below, I couldn't find any examples how can I do it. Only main_test.go but it is missing main.go and for me, it isn't obvious how can I use it. I also went through Github issues but I can not find anything helpful.

Function:

import (
  "fmt"
  "k8s.io/api/core/v1"
  metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
  fake "k8s.io/client-go/kubernetes/fake"
  "time"
)

func GetNamespaceCreationTime(namespace string) int64 {
    config, err := rest.InClusterConfig()
    if err != nil {
        panic(err.Error())
    }
    clientset, err := kubernetes.NewForConfig(config)
    if err != nil {
        panic(err.Error())
    }

    ns, err := clientset.CoreV1().Namespaces().Get(namespace, metav1.GetOptions{})
    if err != nil {
        panic(err.Error())
    }
    fmt.Printf("%v \n", ns.CreationTimestamp)
    return (ns.GetCreationTimestamp().Unix())
}

Test:

I think my test should look like below, but how can I use config := fake.NewSimpleClientset(), should I pass it into GetNamespaceCreationTime function?

func TestGetNamespaceCreationTime(t *testing.T) {
  config := fake.NewSimpleClientset()
  got := GetNamespaceCreationTime("default")
  want := int64(1257894000)

  nsMock := config.CoreV1().Namespaces()
  nsMock.Create(&v1.Namespace{
    ObjectMeta: metav1.ObjectMeta{
      Name:              "default",
      CreationTimestamp: metav1.Date(2009, time.November, 10, 23, 0, 0, 0, time.UTC),
    },
  })

  if got != want {
    t.Errorf("got %q want %q", got, want)
  }

Answer 1

You need to move the initialization part outside the GetNamespaceCreationTime function. You can pass the kubernetes.Interface as a parameter to that function.

    import (
      "fmt"
      "k8s.io/api/core/v1"
      metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
      fake "k8s.io/client-go/kubernetes/fake"
      "k8s.io/client-go/kubernetes"
      "time"
    )

var getInclusterConfigFunc = rest.InClusterConfig
var getNewKubeClientFunc = dynamic.NewForConfig
   
    
    func GetNamespaceCreationTime(kubeClient kubernetes.Interface, namespace string) int64 {
    
        ns, err := kubeClient.CoreV1().Namespaces().Get(namespace, metav1.GetOptions{})
        if err != nil {
            panic(err.Error())
        }
        fmt.Printf("%v \n", ns.CreationTimestamp)
        return (ns.GetCreationTimestamp().Unix())
    }
    
    func GetClientSet() kubernetes.Interface {
      config, err := getInclusterConfigFunc()
      if err != nil {
        log.Warnf("Could not get in-cluster config: %s", err)
        return nil, err
      }

      client, err := getNewKubeClientFunc(config)
      if err != nil {
        log.Warnf("Could not connect to in-cluster API server: %s", err)
        return nil, err
      }

      return client, err
    }

Then your test function can instantiate the fake client and call the method.

    func TestGetNamespaceCreationTime(t *testing.T) {
      kubeClient := fake.NewSimpleClientset()
      got := GetNamespaceCreationTime(kubeClient, "default")
      want := int64(1257894000)
    
      nsMock := config.CoreV1().Namespaces()
      nsMock.Create(&v1.Namespace{
        ObjectMeta: metav1.ObjectMeta{
          Name:              "default",
          CreationTimestamp: metav1.Date(2009, time.November, 10, 23, 0, 0, 0, time.UTC),
        },
      })
    
      if got != want {
        t.Errorf("got %q want %q", got, want)
      }

func fakeGetInclusterConfig() (*rest.Config, error) {
    return nil, nil
}

func fakeGetInclusterConfigWithError() (*rest.Config, error) {
    return nil, errors.New("fake error getting in-cluster config")
}

func TestGetInclusterKubeClient(t *testing.T) {
    origGetInclusterConfig := getInclusterConfigFunc
    getInclusterConfigFunc = fakeGetInclusterConfig
    origGetNewKubeClient := getNewKubeClientFunc
    getNewKubeClientFunc = fakeGetNewKubeClient

    defer func() {
        getInclusterConfigFunc = origGetInclusterConfig
        getNewKubeClientFunc = origGetNewKubeClient
    }()

    client, err := GetClientSet()
    assert.Nil(t, client, "Client is not nil")
    assert.Nil(t, err, "error is not nil")
}

func TestGetInclusterKubeClient_ConfigError(t *testing.T) {
    origGetInclusterConfig := getInclusterConfigFunc
    getInclusterConfigFunc = fakeGetInclusterConfigWithError

    defer func() {
        getInclusterConfigFunc = origGetInclusterConfig
    }()

    client, err := GetInclusterKubeClient()
    assert.Nil(t, client, "Client is not nil")
    assert.NotNil(t, err, "error is nil")
}