diff --git a/src/test/java/com/example/baispolicy/PaymentServiceTest.java b/src/test/java/com/example/baispolicy/PaymentServiceTest.java
new file mode 100644
index 0000000..e29ee02
--- /dev/null
+++ b/src/test/java/com/example/baispolicy/PaymentServiceTest.java
@@ -0,0 +1,25 @@
+package com.example.baispolicy;
+
+import org.junit.jupiter.api.Test;
+import static org.junit.jupiter.api.Assertions.*;
+
+class PaymentServiceTest {
+    private final PaymentService paymentService = new PaymentService();
+
+    @Test
+    void testApprove_WithValidTransactionId_ShouldReturnApprovedMessage() {
+        String transactionId = "12345";
+        String result = paymentService.approve(transactionId);
+        assertEquals("APPROVED:12345", result);
+    }
+
+    @Test
+    void testApprove_WithBlankTransactionId_ShouldThrowException() {
+        assertThrows(IllegalArgumentException.class, () -> {
+            paymentService.approve("");
+        });
+        assertThrows(IllegalArgumentException.class, () -> {
+            paymentService.approve(null);
+        });
+    }
+}