envtest: export DefaultKubeAPIServerFlags & make it configurable

This change exports DefaultKubeAPIServerFlags, allowing a user to
append the default flags with other custom flags and set it to
Environment.KubeAPIServerFlags.
If KubeAPIServerFlags is not set, DefaultKubeAPIServerFlags is used when
the API server starts.

pkg/envtest/server.go

@@ -52,9 +52,8 @@ func defaultAssetPath(binary string) string {
 
 }
 
-// APIServerDefaultArgs are flags necessary to bring up apiserver.
-// TODO: create test framework interface to append flag to default flags.
-var defaultKubeAPIServerFlags = []string{
+// DefaultKubeAPIServerFlags are default flags necessary to bring up apiserver.
+var DefaultKubeAPIServerFlags = []string{
 	"--etcd-servers={{ if .EtcdURL }}{{ .EtcdURL.String }}{{ end }}",
 	"--cert-dir={{ .CertDir }}",
 	"--insecure-port={{ if .URL }}{{ .URL.Port }}{{ end }}",
@@ -92,6 +91,9 @@ type Environment struct {
 	// may take to stop. It defaults to the KUBEBUILDER_CONTROLPLANE_STOP_TIMEOUT
 	// environment variable or 20 seconds if unspecified
 	ControlPlaneStopTimeout time.Duration
+
+	// KubeAPIServerFlags is the set of flags passed while starting the api server.
+	KubeAPIServerFlags []string
 }
 
 // Stop stops a running server
@@ -102,6 +104,15 @@ func (te *Environment) Stop() error {
 	return te.ControlPlane.Stop()
 }
 
+// getAPIServerFlags returns flags to be used with the Kubernetes API server.
+func (te Environment) getAPIServerFlags() []string {
+	// Set default API server flags if not set.
+	if len(te.KubeAPIServerFlags) == 0 {
+		return DefaultKubeAPIServerFlags
+	}
+	return te.KubeAPIServerFlags
+}
+
 // Start starts a local Kubernetes server and updates te.ApiserverPort with the port it is listening on
 func (te *Environment) Start() (*rest.Config, error) {
 	if te.UseExistingCluster {
@@ -117,8 +128,7 @@ func (te *Environment) Start() (*rest.Config, error) {
 		}
 	} else {
 		te.ControlPlane = integration.ControlPlane{}
-		te.ControlPlane.APIServer = &integration.APIServer{Args: defaultKubeAPIServerFlags}
-
+		te.ControlPlane.APIServer = &integration.APIServer{Args: te.getAPIServerFlags()}
 		if os.Getenv(envKubeAPIServerBin) == "" {
 			te.ControlPlane.APIServer.Path = defaultAssetPath("kube-apiserver")
 		}