test: add DTO validation and JSON tests (create/update request, create response, dto)

Author: barissayli

customer-service/src/test/java/io/github/bsayli/customerservice/api/dto/CustomerCreateRequestValidationTest.java

@@ -0,0 +1,42 @@
+package io.github.bsayli.customerservice.api.dto;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import jakarta.validation.Validation;
+import jakarta.validation.Validator;
+import jakarta.validation.ValidatorFactory;
+import org.junit.jupiter.api.*;
+
+@Tag("unit")
+@DisplayName("DTO Validation: CustomerCreateRequest")
+class CustomerCreateRequestValidationTest {
+
+  private static Validator validator;
+
+  @BeforeAll
+  static void setup() {
+    ValidatorFactory factory = Validation.buildDefaultValidatorFactory();
+    validator = factory.getValidator();
+  }
+
+  @Test
+  @DisplayName("name/email valid -> no violations")
+  void validPayload_shouldPass() {
+    var dto = new CustomerCreateRequest("John Smith", "john.smith@example.com");
+    assertThat(validator.validate(dto)).isEmpty();
+  }
+
+  @Test
+  @DisplayName("blank name -> validation fails")
+  void blankName_shouldFail() {
+    var dto = new CustomerCreateRequest("  ", "john.smith@example.com");
+    assertThat(validator.validate(dto)).isNotEmpty();
+  }
+
+  @Test
+  @DisplayName("invalid email -> validation fails")
+  void invalidEmail_shouldFail() {
+    var dto = new CustomerCreateRequest("John Smith", "not-an-email");
+    assertThat(validator.validate(dto)).isNotEmpty();
+  }
+}

customer-service/src/test/java/io/github/bsayli/customerservice/api/dto/CustomerCreateResponseJsonTest.java

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+package io.github.bsayli.customerservice.api.dto;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.SerializationFeature;
+import com.fasterxml.jackson.datatype.jsr310.JavaTimeModule;
+import java.time.Instant;
+import org.junit.jupiter.api.*;
+
+@Tag("unit")
+@DisplayName("DTO JSON: CustomerCreateResponse")
+class CustomerCreateResponseJsonTest {
+
+  private ObjectMapper om;
+
+  @BeforeEach
+  void setUp() {
+    om = new ObjectMapper();
+    om.registerModule(new JavaTimeModule());
+    om.disable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS);
+  }
+
+  @Test
+  @DisplayName("createdAt should serialize as ISO-8601 string")
+  void createdAt_shouldBeIso8601() throws Exception {
+    var customer = new CustomerDto(10, "Jane", "jane@example.com");
+    var resp = new CustomerCreateResponse(customer, Instant.parse("2025-01-01T12:34:56Z"));
+
+    String json = om.writeValueAsString(resp);
+    assertThat(json).contains("\"createdAt\":\"2025-01-01T12:34:56Z\"");
+  }
+}

customer-service/src/test/java/io/github/bsayli/customerservice/api/dto/CustomerDtoJsonTest.java

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+package io.github.bsayli.customerservice.api.dto;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.datatype.jsr310.JavaTimeModule;
+import org.junit.jupiter.api.*;
+
+@Tag("unit")
+@DisplayName("DTO JSON: CustomerDto")
+class CustomerDtoJsonTest {
+
+  private ObjectMapper om;
+
+  @BeforeEach
+  void setUp() {
+    om = new ObjectMapper();
+    om.registerModule(new JavaTimeModule());
+  }
+
+  @Test
+  @DisplayName("serialize/deserialize should preserve fields")
+  void roundTrip_shouldPreserveFields() throws Exception {
+    var dto = new CustomerDto(5, "Mark Lee", "mark.lee@example.com");
+
+    String json = om.writeValueAsString(dto);
+    CustomerDto back = om.readValue(json, CustomerDto.class);
+
+    assertThat(back.customerId()).isEqualTo(5);
+    assertThat(back.name()).isEqualTo("Mark Lee");
+    assertThat(back.email()).isEqualTo("mark.lee@example.com");
+  }
+}

customer-service/src/test/java/io/github/bsayli/customerservice/api/dto/CustomerUpdateRequestValidationTest.java

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+package io.github.bsayli.customerservice.api.dto;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import jakarta.validation.Validation;
+import jakarta.validation.Validator;
+import jakarta.validation.ValidatorFactory;
+import org.junit.jupiter.api.*;
+
+@Tag("unit")
+@DisplayName("DTO Validation: CustomerUpdateRequest")
+class CustomerUpdateRequestValidationTest {
+
+  private static Validator validator;
+
+  @BeforeAll
+  static void setup() {
+    ValidatorFactory factory = Validation.buildDefaultValidatorFactory();
+    validator = factory.getValidator();
+  }
+
+  @Test
+  @DisplayName("valid update -> no violations")
+  void validUpdate_shouldPass() {
+    var dto = new CustomerUpdateRequest("Jane Doe", "jane.doe@example.com");
+    assertThat(validator.validate(dto)).isEmpty();
+  }
+
+  @Test
+  @DisplayName("blank name or invalid email -> violations")
+  void invalidUpdate_shouldFail() {
+    var dto1 = new CustomerUpdateRequest("", "jane.doe@example.com");
+    var dto2 = new CustomerUpdateRequest("Jane Doe", "bad-email");
+    assertThat(validator.validate(dto1)).isNotEmpty();
+    assertThat(validator.validate(dto2)).isNotEmpty();
+  }
+}