Article title exists error message

src/main/java/io/spring/api/ArticlesApi.java

@@ -44,6 +44,11 @@ public class ArticlesApi {
             throw new InvalidRequestException(bindingResult);
         }
 
+        if (articleQueryService.findBySlug(Article.toSlug(newArticleParam.getTitle()), null).isPresent()) {
+            bindingResult.rejectValue("title", "DUPLICATED", "article name exists");
+            throw new InvalidRequestException(bindingResult);
+        }
+
         Article article = new Article(
             newArticleParam.getTitle(),
             newArticleParam.getDescription(),

src/main/java/io/spring/core/article/Article.java

@@ -56,7 +56,7 @@ public class Article {
         this.updatedAt = new DateTime();
     }
 
-    private String toSlug(String title) {
+    public static String toSlug(String title) {
         return title.toLowerCase().replaceAll("[\\&|[\\uFE30-\\uFFA0]|\\’|\\”|\\s\\?\\,\\.]+", "-");
     }
 }

src/test/java/io/spring/api/ArticlesApiTest.java

@@ -6,6 +6,7 @@ import io.spring.api.security.WebSecurityConfig;
 import io.spring.application.ArticleQueryService;
 import io.spring.application.data.ArticleData;
 import io.spring.application.data.ProfileData;
+import io.spring.core.article.Article;
 import io.spring.core.article.ArticleRepository;
 import org.joda.time.DateTime;
 import org.junit.Before;
@@ -24,6 +25,8 @@ import java.util.Optional;
 import static io.restassured.module.mockmvc.RestAssuredMockMvc.given;
 import static org.hamcrest.core.IsEqual.equalTo;
 import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.ArgumentMatchers.eq;
+import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.when;
 
@@ -68,6 +71,8 @@ public class ArticlesApiTest extends TestWithCurrentUser {
             Arrays.asList(tagList),
             new ProfileData("userid", user.getUsername(), user.getBio(), user.getImage(), false));
 
+        when(articleQueryService.findBySlug(eq(Article.toSlug(title)), any())).thenReturn(Optional.empty());
+
         when(articleQueryService.findById(any(), any())).thenReturn(Optional.of(articleData));
 
         given()
@@ -109,6 +114,43 @@ public class ArticlesApiTest extends TestWithCurrentUser {
 
     }
 
+    @Test
+    public void should_get_error_message_with_duplicated_title() {
+        String title = "How to train your dragon";
+        String slug = "how-to-train-your-dragon";
+        String description = "Ever wonder how?";
+        String body = "You have to believe";
+        String[] tagList = {"reactjs", "angularjs", "dragons"};
+        Map<String, Object> param = prepareParam(title, description, body, tagList);
+
+        ArticleData articleData = new ArticleData(
+            "123",
+            slug,
+            title,
+            description,
+            body,
+            false,
+            0,
+            new DateTime(),
+            new DateTime(),
+            Arrays.asList(tagList),
+            new ProfileData("userid", user.getUsername(), user.getBio(), user.getImage(), false));
+
+        when(articleQueryService.findBySlug(eq(Article.toSlug(title)), any())).thenReturn(Optional.of(articleData));
+
+        when(articleQueryService.findById(any(), any())).thenReturn(Optional.of(articleData));
+
+        given()
+            .contentType("application/json")
+            .header("Authorization", "Token " + token)
+            .body(param)
+            .when()
+            .post("/articles")
+            .then()
+            .statusCode(422);
+
+    }
+
     private HashMap<String, Object> prepareParam(final String title, final String description, final String body, final String[] tagList) {
         return new HashMap<String, Object>() {{
             put("article", new HashMap<String, Object>() {{