build: add unit test, improve code coverage

Author: jknack

jooby/pom.xml

@@ -95,6 +95,11 @@
       <version>3.4.15</version>
       <scope>test</scope>
     </dependency>
+    <dependency>
+      <groupId>org.mockito</groupId>
+      <artifactId>mockito-junit-jupiter</artifactId>
+      <scope>test</scope>
+    </dependency>
   </dependencies>
 
   <build>