diff --git a/metropolis/pkg/pki/certificate_test.go b/metropolis/pkg/pki/certificate_test.go
new file mode 100644
index 0000000..da8dee9
--- /dev/null
+++ b/metropolis/pkg/pki/certificate_test.go
@@ -0,0 +1,172 @@
+package pki
+
+import (
+	"bytes"
+	"context"
+	"crypto/ed25519"
+	"crypto/rand"
+	"crypto/x509"
+	"testing"
+
+	"go.etcd.io/etcd/integration"
+)
+
+// TestManaged ensures Managed Certificates work, including re-ensuring
+// certificates with the same data and issuing subordinate certificates.
+func TestManaged(t *testing.T) {
+	cluster := integration.NewClusterV3(nil, &integration.ClusterConfig{
+		Size: 1,
+	})
+	cl := cluster.Client(0)
+	defer cluster.Terminate(nil)
+	ctx, ctxC := context.WithCancel(context.Background())
+	defer ctxC()
+	ns := Namespaced("/test-managed/")
+
+	// Test CA certificate issuance.
+	ca := &Certificate{
+		Namespace: &ns,
+		Issuer:    SelfSigned,
+		Name:      "ca",
+		Template:  CA("Test CA"),
+	}
+	caBytes, err := ca.Ensure(ctx, cl)
+	if err != nil {
+		t.Fatalf("Failed to Ensure CA: %v", err)
+	}
+	caCert, err := x509.ParseCertificate(caBytes)
+	if err != nil {
+		t.Fatalf("Failed to parse newly emited CA cert: %v", err)
+	}
+	if !caCert.IsCA {
+		t.Errorf("Newly emitted CA cert is not CA")
+	}
+	if ca.PublicKey == nil {
+		t.Errorf("Newly emitted CA cert has no public key")
+	}
+	if ca.PrivateKey == nil {
+		t.Errorf("Newly emitted CA cert has no public key")
+	}
+
+	// Re-emitting CA certificate with same parameters should return exact same
+	// data.
+	ca2 := &Certificate{
+		Namespace: &ns,
+		Issuer:    SelfSigned,
+		Name:      "ca",
+		Template:  CA("Test CA"),
+	}
+	caBytes2, err := ca2.Ensure(ctx, cl)
+	if err != nil {
+		t.Fatalf("Failed to re-Ensure CA: %v", err)
+	}
+	if !bytes.Equal(caBytes, caBytes2) {
+		t.Errorf("New CA has different x509 certificate")
+	}
+	if !bytes.Equal(ca.PublicKey, ca2.PublicKey) {
+		t.Errorf("New CA has different public key")
+	}
+	if !bytes.Equal(ca.PrivateKey, ca2.PrivateKey) {
+		t.Errorf("New CA has different private key")
+	}
+
+	// Emitting a subordinate certificate should work.
+	client := &Certificate{
+		Namespace: &ns,
+		Issuer:    ca2,
+		Name:      "client",
+		Template:  Client("foo", nil),
+	}
+	clientBytes, err := client.Ensure(ctx, cl)
+	if err != nil {
+		t.Fatalf("Failed to ensure client certificate: %v", err)
+	}
+	clientCert, err := x509.ParseCertificate(clientBytes)
+	if err != nil {
+		t.Fatalf("Failed to parse newly emitted client certificate: %v", err)
+	}
+	if clientCert.IsCA {
+		t.Errorf("New client cert is CA")
+	}
+	if want, got := "foo", clientCert.Subject.CommonName; want != got {
+		t.Errorf("New client CN should be %q, got %q", want, got)
+	}
+	if want, got := caCert.Subject.String(), clientCert.Issuer.String(); want != got {
+		t.Errorf("New client issuer should be %q, got %q", want, got)
+	}
+}
+
+// TestExternal ensures External certificates work correctly, including
+// re-Ensuring certificates with the same public key, and attempting to re-issue
+// the same certificate with a different public key (which should fail).
+func TestExternal(t *testing.T) {
+	cluster := integration.NewClusterV3(nil, &integration.ClusterConfig{
+		Size: 1,
+	})
+	cl := cluster.Client(0)
+	defer cluster.Terminate(nil)
+	ctx, ctxC := context.WithCancel(context.Background())
+	defer ctxC()
+	ns := Namespaced("/test-external/")
+
+	ca := &Certificate{
+		Namespace: &ns,
+		Issuer:    SelfSigned,
+		Name:      "ca",
+		Template:  CA("Test CA"),
+	}
+
+	// Issuing an external certificate should work.
+	pk, _, err := ed25519.GenerateKey(rand.Reader)
+	if err != nil {
+		t.Fatalf("GenerateKey: %v", err)
+	}
+	server := &Certificate{
+		Namespace: &ns,
+		Issuer:    ca,
+		Name:      "server",
+		Template:  Server([]string{"server"}, nil),
+		Mode:      CertificateExternal,
+		PublicKey: pk,
+	}
+	serverBytes, err := server.Ensure(ctx, cl)
+	if err != nil {
+		t.Fatalf("Failed to Ensure server certificate: %v", err)
+	}
+
+	// Issuing an external certificate with the same name but different public key
+	// should fail.
+	pk2, _, err := ed25519.GenerateKey(rand.Reader)
+	if err != nil {
+		t.Fatalf("GenerateKey: %v", err)
+	}
+	server2 := &Certificate{
+		Namespace: &ns,
+		Issuer:    ca,
+		Name:      "server",
+		Template:  Server([]string{"server"}, nil),
+		Mode:      CertificateExternal,
+		PublicKey: pk2,
+	}
+	if _, err := server2.Ensure(ctx, cl); err == nil {
+		t.Fatalf("Issuing server certificate with different public key should have failed")
+	}
+
+	// Issuing the external certificate with the same name and same public key
+	// should work and yield the same x509 bytes.
+	server3 := &Certificate{
+		Namespace: &ns,
+		Issuer:    ca,
+		Name:      "server",
+		Template:  Server([]string{"server"}, nil),
+		Mode:      CertificateExternal,
+		PublicKey: pk,
+	}
+	serverBytes3, err := server3.Ensure(ctx, cl)
+	if err != nil {
+		t.Fatalf("Failed to re-Ensure server certificate: %v", err)
+	}
+	if !bytes.Equal(serverBytes, serverBytes3) {
+		t.Errorf("New server certificate has different x509 certificate")
+	}
+}