Add RestExceptionHandler test

src/Server/src/main/java/greenify/server/rest/RestExceptionHandler.java

@@ -11,7 +11,7 @@ import org.springframework.web.bind.annotation.RestControllerAdvice;
 public class RestExceptionHandler {
     @ExceptionHandler(ApplicationException.class)
     @ResponseStatus(HttpStatus.BAD_REQUEST)
-    public ErrorResponse applicationException(ApplicationException ex) {
+    public static ErrorResponse applicationException(ApplicationException ex) {
         return new ErrorResponse(ex.getMessage());
     }
 }

src/Server/src/test/java/greenify/server/rest/RestExceptionHandlerTest.java

@@ -0,0 +1,17 @@
+package greenify.server.rest;
+
+import static org.junit.Assert.assertEquals;
+
+import greenify.common.ApplicationException;
+import greenify.common.ErrorResponse;
+import org.junit.Test;
+
+public class RestExceptionHandlerTest {
+    @Test
+    public void test() {
+        ApplicationException ex = new ApplicationException("testing");
+        ErrorResponse response = new ErrorResponse("testing");
+        assertEquals(RestExceptionHandler.applicationException(ex)
+                .getMessage(), response.getMessage());
+    }
+}