diff --git a/operator/controllers/replicas_test.go b/operator/controllers/replicas_test.go
new file mode 100644
index 0000000000..76183f97f2
--- /dev/null
+++ b/operator/controllers/replicas_test.go
@@ -0,0 +1,119 @@
+package controllers
+
+import (
+	. "github.com/onsi/gomega"
+	machinelearningv1 "github.com/seldonio/seldon-core/operator/apis/machinelearning/v1"
+	v1 "k8s.io/api/core/v1"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	ctrl "sigs.k8s.io/controller-runtime"
+	"testing"
+)
+
+func createSeldonDeploymentWithReplicas(name string, namespace string, defaultReplicas *int32, predictorReplicas *int32, componentSpecReplicas *int32, svcOrchReplicas *int32) *machinelearningv1.SeldonDeployment {
+	modelType := machinelearningv1.MODEL
+	instance := &machinelearningv1.SeldonDeployment{
+		ObjectMeta: metav1.ObjectMeta{
+			Name:      name,
+			Namespace: namespace,
+		},
+		Spec: machinelearningv1.SeldonDeploymentSpec{
+			DefaultReplicas: defaultReplicas,
+			Predictors: []machinelearningv1.PredictorSpec{
+				{
+					Name:     "p1",
+					Replicas: predictorReplicas,
+					ComponentSpecs: []*machinelearningv1.SeldonPodSpec{
+						{
+							Metadata: metav1.ObjectMeta{},
+							Replicas: componentSpecReplicas,
+							Spec: v1.PodSpec{
+								Containers: []v1.Container{
+									{
+										Image: "seldonio/mock_classifier:1.0",
+										Name:  "classifier",
+									},
+								},
+							},
+						},
+					},
+					Graph: &machinelearningv1.PredictiveUnit{
+						Name: "classifier",
+						Type: &modelType,
+					},
+				},
+			},
+		},
+	}
+
+	if svcOrchReplicas != nil {
+		instance.Spec.Annotations = map[string]string{machinelearningv1.ANNOTATION_SEPARATE_ENGINE: "true"}
+		instance.Spec.Predictors[0].SvcOrchSpec = machinelearningv1.SvcOrchSpec{
+			Replicas: svcOrchReplicas,
+		}
+	}
+	return instance
+}
+
+func TestDeploymentReplicas(t *testing.T) {
+	g := NewGomegaWithT(t)
+	svcOrchReplicas := int32(2)
+	defaultReplicas := int32(3)
+	predictorReplicas := int32(4)
+	componentSpecReplicas := int32(5)
+	name := "dep"
+	namespace := "default"
+
+	logger := ctrl.Log.WithName("controllers").WithName("SeldonDeployment")
+	reconciler := &SeldonDeploymentReconciler{
+		Log: logger,
+	}
+
+	// Just Predictor Replicas
+	instance := createSeldonDeploymentWithReplicas(name, namespace, nil, &predictorReplicas, nil, nil)
+	instance.Spec.DefaultSeldonDeployment(name, namespace)
+	c, err := reconciler.createComponents(instance, logger)
+	g.Expect(err).To(BeNil())
+	g.Expect(len(c.deployments)).To(Equal(1))
+	g.Expect(*c.deployments[0].Spec.Replicas).To(Equal(predictorReplicas))
+
+	// Just Predictor Replicas and default replicas
+	instance = createSeldonDeploymentWithReplicas(name, namespace, &defaultReplicas, &predictorReplicas, nil, nil)
+	instance.Spec.DefaultSeldonDeployment(name, namespace)
+	c, err = reconciler.createComponents(instance, logger)
+	g.Expect(err).To(BeNil())
+	g.Expect(len(c.deployments)).To(Equal(1))
+	g.Expect(*c.deployments[0].Spec.Replicas).To(Equal(predictorReplicas))
+
+	// ComponentSpec replica override
+	instance = createSeldonDeploymentWithReplicas(name, namespace, &defaultReplicas, &predictorReplicas, &componentSpecReplicas, nil)
+	instance.Spec.DefaultSeldonDeployment(name, namespace)
+	c, err = reconciler.createComponents(instance, logger)
+	g.Expect(err).To(BeNil())
+	g.Expect(len(c.deployments)).To(Equal(1))
+	g.Expect(*c.deployments[0].Spec.Replicas).To(Equal(componentSpecReplicas))
+
+	// Just defaultReplicas
+	instance = createSeldonDeploymentWithReplicas(name, namespace, &defaultReplicas, nil, nil, nil)
+	instance.Spec.DefaultSeldonDeployment(name, namespace)
+	c, err = reconciler.createComponents(instance, logger)
+	g.Expect(err).To(BeNil())
+	g.Expect(len(c.deployments)).To(Equal(1))
+	g.Expect(*c.deployments[0].Spec.Replicas).To(Equal(defaultReplicas))
+
+	// All nil
+	instance = createSeldonDeploymentWithReplicas(name, namespace, nil, nil, nil, nil)
+	instance.Spec.DefaultSeldonDeployment(name, namespace)
+	c, err = reconciler.createComponents(instance, logger)
+	g.Expect(err).To(BeNil())
+	g.Expect(len(c.deployments)).To(Equal(1))
+	g.Expect(c.deployments[0].Spec.Replicas).To(BeNil())
+
+	// SvcOrchReplicas
+	instance = createSeldonDeploymentWithReplicas(name, namespace, nil, nil, nil, &svcOrchReplicas)
+	instance.Spec.DefaultSeldonDeployment(name, namespace)
+	c, err = reconciler.createComponents(instance, logger)
+	g.Expect(err).To(BeNil())
+	g.Expect(len(c.deployments)).To(Equal(2))
+	g.Expect(*c.deployments[0].Spec.Replicas).To(Equal(svcOrchReplicas))
+	g.Expect(c.deployments[1].Spec.Replicas).To(BeNil())
+}