test: add unit and integration tests

domain/pom.xml

@@ -21,5 +21,33 @@
             <artifactId>slf4j-api</artifactId>
             <version>2.0.13</version>
         </dependency>
+
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter</artifactId>
+            <version>5.10.0</version>
+            <scope>test</scope>
+        </dependency>
+
+        <dependency>
+            <groupId>org.mockito</groupId>
+            <artifactId>mockito-core</artifactId>
+            <version>5.14.2</version>
+            <scope>test</scope>
+        </dependency>
+
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>3.24.2</version>
+            <scope>test</scope>
+        </dependency>
     </dependencies>
+    <repositories>
+        <repository>
+            <id>maven_central</id>
+            <name>Maven Central</name>
+            <url>https://repo.maven.apache.org/maven2/</url>
+        </repository>
+    </repositories>
 </project>

domain/src/test/java/com/pablotj/restemailbridge/domain/service/EmailValidatorServiceTest.java

@@ -0,0 +1,62 @@
+package com.pablotj.restemailbridge.domain.service;
+
+import com.pablotj.restemailbridge.domain.model.Email;
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+
+class EmailValidatorServiceTest {
+
+    private final EmailValidatorService validator = new EmailValidatorService();
+
+    @Test
+    void shouldThrowIfEmailIsNull() {
+        assertThatThrownBy(() -> validator.validate(null))
+                .isInstanceOf(IllegalArgumentException.class)
+                .hasMessage("Email cannot be null");
+    }
+
+    @Test
+    void shouldThrowIfRecipientInvalid() {
+        Email email = Email.create("sender@example.com", "not-an-email", "Subject", "Body");
+
+        assertThatThrownBy(() -> validator.validate(email))
+                .isInstanceOf(IllegalArgumentException.class)
+                .hasMessage("Recipient email is invalid");
+    }
+
+    @Test
+    void shouldThrowIfSenderIsBlank() {
+        Email email = Email.create("", "recipient@example.com", "Subject", "Body");
+
+        assertThatThrownBy(() -> validator.validate(email))
+                .isInstanceOf(IllegalArgumentException.class)
+                .hasMessage("Sender email is required");
+    }
+
+    @Test
+    void shouldThrowIfSubjectIsBlank() {
+        Email email = Email.create("sender@example.com", "recipient@example.com", "", "Body");
+
+        assertThatThrownBy(() -> validator.validate(email))
+                .isInstanceOf(IllegalArgumentException.class)
+                .hasMessage("Subject is required");
+    }
+
+    @Test
+    void shouldThrowIfBodyIsBlank() {
+        Email email = Email.create("sender@example.com", "recipient@example.com", "Subject", "");
+
+        assertThatThrownBy(() -> validator.validate(email))
+                .isInstanceOf(IllegalArgumentException.class)
+                .hasMessage("Body is required");
+    }
+
+    @Test
+    void shouldPassForValidEmail() {
+        Email email = Email.create("sender@example.com", "recipient@example.com", "Subject", "Body");
+
+        // no debe lanzar excepción
+        validator.validate(email);
+    }
+}