diff --git a/ln/ln_test.go b/ln/ln_test.go
new file mode 100644
index 0000000..19fd162
--- /dev/null
+++ b/ln/ln_test.go
@@ -0,0 +1,22 @@
+package ln_test
+
+import (
+	"testing"
+
+	"github.com/philippgille/ln-paywall/ln"
+)
+
+// TestHashPreimage tests if the result of the HashPreimage function is correct.
+func TestHashPreimage(t *testing.T) {
+	// Correct preimage form, taken from an invoice JSON in lnd
+	preimage := "CtkknKfJ237o8jbippg5NziFZgkUvk9cN20NCuPvqxQ="
+	// Taken from the same invoice JSON in lnd
+	expected := "iYYYRTzq0XZgBo1aIAv4KZTzq1PCTmf6nnWvyHMB4C0="
+	actual, err := ln.HashPreimage(preimage)
+	if err != nil {
+		t.Errorf("An error occurred during the test: %v\n", err)
+	}
+	if actual != expected {
+		t.Errorf("Expected %v, but was %v\n", expected, actual)
+	}
+}