Create test utils for crafting kubeconfig strings

Signed-off-by: Ahmet Alp Balkan <ahmetb@google.com>

internal/testutil/kubeconfigbuilder.go

@@ -0,0 +1,36 @@
+package testutil
+
+import (
+	"strings"
+	"testing"
+
+	"gopkg.in/yaml.v3"
+)
+
+type Context struct {
+	Name      string `yaml:"name,omitempty"`
+	Namespace string `yaml:"namespace,omitempty"`
+}
+
+func Ctx(name string) *Context { return &Context{Name: name} }
+
+type Kubeconfig map[string]interface{}
+
+func KC() *Kubeconfig {
+	return &Kubeconfig{
+		"apiVersion": "v1",
+		"kind":       "Config"}
+}
+
+func (k *Kubeconfig) Set(key string, v interface{}) *Kubeconfig { (*k)[key] = v; return k }
+func (k *Kubeconfig) WithCurrentCtx(s string) *Kubeconfig       { (*k)["current-context"] = s; return k }
+func (k *Kubeconfig) WithCtxs(c ...*Context) *Kubeconfig        { (*k)["contexts"] = c; return k }
+
+func (k *Kubeconfig) ToYAML(t *testing.T) string {
+	t.Helper()
+	var v strings.Builder
+	if err := yaml.NewEncoder(&v).Encode(*k); err != nil {
+		t.Fatalf("failed to encode mock kubeconfig: %v", err)
+	}
+	return v.String()
+}