test: Add FormatterTest.

Change-Id: Id627819583e8c9867b3950b7d8aac6830e5f3f80
diff --git a/core/pom.xml b/core/pom.xml
index cb61c20..a75acd5 100644
--- a/core/pom.xml
+++ b/core/pom.xml
@@ -42,6 +42,19 @@
       <artifactId>parsson</artifactId>
       <version>1.1.6</version>
     </dependency>
+
+    <dependency>
+      <groupId>org.junit.jupiter</groupId>
+      <artifactId>junit-jupiter-engine</artifactId>
+      <version>5.10.2</version>
+      <scope>test</scope>
+    </dependency>
+    <dependency>
+      <groupId>org.junit.jupiter</groupId>
+      <artifactId>junit-jupiter-api</artifactId>
+      <version>5.10.2</version>
+      <scope>test</scope>
+    </dependency>
   </dependencies>
 
   <build>
@@ -58,6 +71,11 @@
         </configuration>
       </plugin>
 
+      <plugin>
+        <artifactId>maven-surefire-plugin</artifactId>
+        <version>3.2.5</version>
+      </plugin>
+
     </plugins>
   </build>