src/test/java/com/example/baisgate/PaymentServiceTest.java

@@ -0,0 +1,32 @@
+package com.example.baisgate;
+
+import org.junit.jupiter.api.Test;
+import static org.junit.jupiter.api.Assertions.*;
+
+class PaymentServiceTest {
+
+    @Test
+    void testApprove_WithValidTransactionId_ReturnsApproved() {
+        PaymentService paymentService = new PaymentService();
+        String result = paymentService.approve("12345");
+        assertEquals("APPROVED:12345", result);
+    }
+
+    @Test
+    void testApprove_WithBlankTransactionId_ThrowsIllegalArgumentException() {
+        PaymentService paymentService = new PaymentService();
+        Exception exception = assertThrows(IllegalArgumentException.class, () -> {
+            paymentService.approve("");
+        });
+        assertEquals("Transaction ID cannot be blank", exception.getMessage());
+    }
+
+    @Test
+    void testApprove_WithNullTransactionId_ThrowsIllegalArgumentException() {
+        PaymentService paymentService = new PaymentService();
+        Exception exception = assertThrows(IllegalArgumentException.class, () -> {
+            paymentService.approve(null);
+        });
+        assertEquals("Transaction ID cannot be blank", exception.getMessage());
+    }
+}