diff --git a/services/payments/src/test/java/com/klaro/bais/payments/PaymentReferenceServiceTest.java b/services/payments/src/test/java/com/klaro/bais/payments/PaymentReferenceServiceTest.java
new file mode 100644
index 0000000..77624c9
--- /dev/null
+++ b/services/payments/src/test/java/com/klaro/bais/payments/PaymentReferenceServiceTest.java
@@ -0,0 +1,28 @@
+package com.klaro.bais.payments;
+
+import org.junit.jupiter.api.Test;
+import static org.junit.jupiter.api.Assertions.*;
+
+class PaymentReferenceServiceTest {
+    private final PaymentReferenceService service = new PaymentReferenceService();
+
+    @Test
+    void testNormalize_NullInput() {
+        assertEquals("", service.normalize(null));
+    }
+
+    @Test
+    void testNormalize_EmptyInput() {
+        assertEquals("", service.normalize(""));
+    }
+
+    @Test
+    void testNormalize_WhitespaceInput() {
+        assertEquals("", service.normalize("   "));
+    }
+
+    @Test
+    void testNormalize_ValidInput() {
+        assertEquals("valid", service.normalize(" valid "));
+    }
+}
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