test: add unit and integration tests

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);
+    }
+}