e2e: don't pass client via globvar

Use the kube-native way to construct a client by using the KUBECONFIG
env var. That was done in the tests anyway (see the change to the
Makefile).

Makefile

@@ -97,7 +97,7 @@ test-unit:
 	go test -v -race -count=1 $(PKGS)
 
 test-e2e:
-	go test -timeout 55m -v ./test/e2e/ $(TEST_RUN_ARGS) --kubeconfig=$(KUBECONFIG)
+	go test -timeout 55m -v ./test/e2e/ $(TEST_RUN_ARGS)
 
 test-local-setup: VERSION = local
 test-local-setup: VERSION_SEMVER = $(shell cat VERSION)

go.mod

@@ -8,6 +8,7 @@ require (
 	github.com/oklog/run v1.1.0
 	github.com/spf13/cobra v1.8.1
 	github.com/spf13/pflag v1.0.5
+	github.com/stretchr/testify v1.9.0
 	golang.org/x/net v0.28.0
 	gopkg.in/yaml.v2 v2.4.0
 	k8s.io/api v0.31.0
@@ -59,6 +60,7 @@ require (
 	github.com/modern-go/reflect2 v1.0.2 // indirect
 	github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822 // indirect
 	github.com/pkg/errors v0.9.1 // indirect
+	github.com/pmezard/go-difflib v1.0.1-0.20181226105442-5d4384ee4fb2 // indirect
 	github.com/pquerna/cachecontrol v0.1.0 // indirect
 	github.com/prometheus/client_golang v1.19.1 // indirect
 	github.com/prometheus/client_model v0.6.1 // indirect

test/e2e/main_test.go

@@ -17,39 +17,25 @@ limitations under the License.
 package e2e
 
 import (
-	"flag"
-	"log"
-	"os"
+	"fmt"
 	"testing"
 
+	"github.com/stretchr/testify/require"
+
 	"k8s.io/client-go/kubernetes"
+	"k8s.io/client-go/rest"
+	"k8s.io/client-go/tools/clientcmd"
 
 	"github.com/brancz/kube-rbac-proxy/test/kubetest"
 )
 
-// Sadly there's no way to pass the k8s client from TestMain to Test,
-// so we need this global instance
-var client kubernetes.Interface
-
-// TestMain adds the kubeconfig flag to our tests
-func TestMain(m *testing.M) {
-	kubeconfig := flag.String(
-		"kubeconfig",
-		"",
-		"path to kubeconfig",
-	)
-	flag.Parse()
-
-	var err error
-	client, err = kubetest.NewClientFromKubeconfig(*kubeconfig)
+func Test(t *testing.T) {
+	clientConfig := newClientConfigForTest(t)
+	client, err := kubernetes.NewForConfig(clientConfig)
 	if err != nil {
-		log.Fatal(err)
+		t.Fatalf("failed to setup a client for the tests: %v", err)
 	}
 
-	os.Exit(m.Run())
-}
-
-func Test(t *testing.T) {
 	tests := map[string]kubetest.TestSuite{
 		"Basics":             testBasics(client),
 		"H2CUpstream":        testH2CUpstream(client),
@@ -68,3 +54,16 @@ func Test(t *testing.T) {
 		t.Run(name, tc)
 	}
 }
+
+// NewClientConfigForTest returns a config configured to connect to the api server
+func newClientConfigForTest(t *testing.T) *rest.Config {
+	loader := clientcmd.NewDefaultClientConfigLoadingRules()
+	clientConfig := clientcmd.NewNonInteractiveDeferredLoadingClientConfig(loader, &clientcmd.ConfigOverrides{})
+	config, err := clientConfig.ClientConfig()
+	if err == nil {
+		fmt.Printf("Found configuration for host %v.\n", config.Host)
+	}
+
+	require.NoError(t, err)
+	return config
+}