diff --git a/test/luna/fs-mem.go b/test/luna/fs-mem.go
index 9f96f7e..06c8ddd 100644
--- a/test/luna/fs-mem.go
+++ b/test/luna/fs-mem.go
@@ -30,6 +30,7 @@ var (
 func NewMemFS() *MemFS {
 	return &MemFS{
 		MapFS: fstest.MapFS{},
+		calc:  &nef.RelativeCalc{},
 	}
 }
 
diff --git a/test/luna/fs-mem_test.go b/test/luna/fs-mem_test.go
index 7400492..afb725c 100644
--- a/test/luna/fs-mem_test.go
+++ b/test/luna/fs-mem_test.go
@@ -15,13 +15,21 @@ var (
 	data = []byte("some content")
 )
 
-var _ = Describe("MemFs", func() {
+var _ = Describe("MemFS", func() {
 	var fS nef.UniversalFS
 
 	BeforeEach(func() {
 		fS = luna.NewMemFS()
 	})
 
+	Context("Calc", func() {
+		When("MemFS is created", func() {
+			It("🧪 should: also be created", func() {
+				Expect(fS.Calc()).NotTo(BeNil())
+			})
+		})
+	})
+
 	Context("Remove", func() {
 		When("given: item exists", func() {
 			It("🧪 should: remove item", func() {