diff --git a/api/internal/plugins/fnplugin/fnplugin_test.go b/api/internal/plugins/fnplugin/fnplugin_test.go
new file mode 100644
index 000000000..0f880d03b
--- /dev/null
+++ b/api/internal/plugins/fnplugin/fnplugin_test.go
@@ -0,0 +1,122 @@
+package fnplugin
+
+import (
+	"bytes"
+	"fmt"
+	"sigs.k8s.io/kustomize/kyaml/kio"
+	"testing"
+)
+
+func TestToResourceList(t *testing.T) {
+	in := []byte(`apiVersion: v1
+data:
+  key1: oldValue
+kind: ConfigMap
+metadata:
+  annotations:
+  kustomize.config.k8s.io/id: |
+    kind: ConfigMap
+    name: config1
+    version: v1
+  name: config1
+---
+apiVersion: v1
+data:
+  key1: oldValue
+kind: ConfigMap
+metadata:
+  annotations:
+  kustomize.config.k8s.io/id: |
+    kind: ConfigMap
+    name: config2
+    version: v1
+  name: config2`)
+	outBuffer, err := toResourceList(in)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	expected := `apiVersion: config.kubernetes.io/v1alpha1
+kind: ResourceList
+items:
+- apiVersion: v1
+  data:
+    key1: oldValue
+  kind: ConfigMap
+  metadata:
+    kustomize.config.k8s.io/id: |
+      kind: ConfigMap
+      name: config1
+      version: v1
+    name: config1
+- apiVersion: v1
+  data:
+    key1: oldValue
+  kind: ConfigMap
+  metadata:
+    kustomize.config.k8s.io/id: |
+      kind: ConfigMap
+      name: config2
+      version: v1
+    name: config2
+`
+
+	if outBuffer.String() != expected {
+		t.Fatalf("output \n%s\n doesn't match expected \n%s\n", outBuffer.String(), expected)
+	}
+}
+
+func TestToResourceListWithEmptyInput(t *testing.T) {
+	expected := fmt.Sprintf("apiVersion: %s\nkind: %s", kio.ResourceListAPIVersion, kio.ResourceListKind)
+	outBuffer, err := toResourceList(nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if outBuffer.String() != expected {
+		t.Fatalf("output \n%s\n doesn't match expected \n%s\n", outBuffer.String(), expected)
+	}
+}
+
+func TestInjectFunctionConfig(t *testing.T) {
+	input := []byte(`apiVersion: config.kubernetes.io/v1alpha1
+kind: ResourceList`)
+	functionConfig, err := bytesToRNode([]byte(`apiVersion: foo-corp.com/v1
+kind: FulfillmentCenter
+metadata:
+  name: staging
+  metadata:
+    annotations:
+      config.k8s.io/function: |
+        container:
+          image: gcr.io/example/foo:v1.0.0
+spec:
+  address: "100 Main St."`))
+	if err != nil {
+		t.Fatal(err)
+	}
+	inputBuffer := bytes.Buffer{}
+	inputBuffer.Write(input)
+	err = injectFunctionConfig(&inputBuffer, functionConfig)
+	if err != nil {
+		t.Fatal(err)
+	}
+	expected := `apiVersion: config.kubernetes.io/v1alpha1
+kind: ResourceList
+functionConfig:
+  apiVersion: foo-corp.com/v1
+  kind: FulfillmentCenter
+  metadata:
+    name: staging
+    metadata:
+      annotations:
+        config.k8s.io/function: |
+          container:
+            image: gcr.io/example/foo:v1.0.0
+  spec:
+    address: "100 Main St."
+`
+
+	if inputBuffer.String() != expected {
+		t.Fatalf("output \n%s\n doesn't match expected \n%s\n", inputBuffer.String(), expected)
+	}
+}