TDD for CashCard contract

src/main/java/djmil/cashcard/CashCard.java

@@ -0,0 +1,5 @@
+package djmil.cashcard;
+
+public record CashCard(Long id, Double amount) {
+    
+}

src/test/java/djmil/cashcard/CashCardJsonTest.java

@@ -1,13 +1,52 @@
 package djmil.cashcard;
 
 import org.junit.jupiter.api.Test;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.autoconfigure.json.JsonTest;
+import org.springframework.boot.test.json.JacksonTester;
+
+import java.io.IOException;
 
 import static org.assertj.core.api.Assertions.assertThat;
 
+@JsonTest
 public class CashCardJsonTest {
 
-@Test
+    @Autowired
+    private JacksonTester<CashCard> json;
+
+    @Test
     public void myFirstTest() {
-        assertThat(1).isEqualTo(42);
+        assertThat(1).isEqualTo(1);
+    }
+
+    @Test
+    public void cashCardSerializationTest() throws IOException {
+        CashCard cashCard = new CashCard(99L, 123.45);
+
+        assertThat(json.write(cashCard)).isStrictlyEqualToJson("expected.json");
+
+        assertThat(json.write(cashCard)).hasJsonPathNumberValue("@.id");
+        assertThat(json.write(cashCard)).extractingJsonPathNumberValue("@.id")
+            .isEqualTo(99);
+
+        assertThat(json.write(cashCard)).hasJsonPathNumberValue("@.amount");
+        assertThat(json.write(cashCard)).extractingJsonPathNumberValue("@.amount")
+            .isEqualTo(123.45);
+    }
+
+    @Test
+    public void cashCardDeserializationTest() throws IOException {
+        String expected = """
+                {
+                    "id":1000,
+                    "amount":67.89
+                }
+                """;
+
+        assertThat(json.parse(expected)).isEqualTo(new CashCard(1000L, 67.89));
+
+        assertThat(json.parseObject(expected).id()).isEqualTo(1000);
+        assertThat(json.parseObject(expected).amount()).isEqualTo(67.89);
     }
 }

src/test/resources/djmil/cashcard/expected.json

@@ -0,0 +1,4 @@
+{
+    "id": 99,
+    "amount": 123.45
+}