Move kubeconfig loader utils to cmdutil pkg

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

internal/kubeconfig/namespace_test.go

@@ -0,0 +1,46 @@
+package kubeconfig
+
+import (
+	"testing"
+
+	"github.com/ahmetb/kubectx/internal/testutil"
+)
+
+func TestKubeconfig_NamespaceOfContext_ctxNotFound(t *testing.T) {
+	kc := new(Kubeconfig).WithLoader(WithMockKubeconfigLoader(testutil.KC().
+		WithCtxs(testutil.Ctx("c1")).ToYAML(t)))
+	if err := kc.Parse(); err != nil {
+		t.Fatal(err)
+	}
+
+	_, err := kc.NamespaceOfContext("c2")
+	if err == nil {
+		t.Fatal("expected err")
+	}
+}
+
+func TestKubeconfig_NamespaceOfContext(t *testing.T) {
+	kc := new(Kubeconfig).WithLoader(WithMockKubeconfigLoader(testutil.KC().
+		WithCtxs(
+			testutil.Ctx("c1"),
+			testutil.Ctx("c2").Ns("c2n1")).ToYAML(t)))
+	if err := kc.Parse(); err != nil {
+		t.Fatal(err)
+	}
+
+	v1, err := kc.NamespaceOfContext("c1")
+	if err != nil {
+		t.Fatal("expected err")
+	}
+	if expected := `default`; v1 != expected {
+		t.Fatalf("c1: expected=%q got=%q", expected, v1)
+	}
+
+	v2, err := kc.NamespaceOfContext("c2")
+	if err != nil {
+		t.Fatal("expected err")
+	}
+	if expected := `c2n1`; v2 != expected {
+		t.Fatalf("c2: expected=%q got=%q", expected, v2)
+	}
+}