Add class composition with mixins examples (#99)

Author: SergeiIonin

scala-core/src/main/scala/com/baeldung/scala/classcompositionwithtraits/CarTraits.scala renamed to scala-core-oop/src/main/scala/com/baeldung/scala/classcompositionwithtraits/CarTraits.scala

@@ -1,7 +1,5 @@
 package com.baeldung.scala.classcompositionwithtraits
 
-import com.baeldung.scala.classcompositionwithtraits.CarTraits.{Car, Printable}
-
 object CarTraits {
 
   /**
@@ -22,6 +20,14 @@ object CarTraits {
   /**
    * Another trait to be mixed into the class
    */
+  trait SimpleMarshaller extends Car {
+    def toJson: String = s"{${"\"model\""}:$model," +
+      s"\n${"\"horsePower\""}:$horsePower}"
+  }
+
+  /**
+   * Another trait with self-type to be mixed into the class
+   */
   trait Marshaller {
     self: Car =>
     def toJson = s"{${"\"model\""}:$model," +

scala-core/src/test/scala/com/baeldung/scala/classcompositionwithtraits/TraitsTest.scala renamed to scala-core-oop/src/test/scala/com/baeldung/scala/classcompositionwithtraits/CarTraitsTest.scala

@@ -1,14 +1,13 @@
 package com.baeldung.scala.classcompositionwithtraits
 
+import com.baeldung.scala.classcompositionwithtraits.CarTraits._
 import org.scalatest.{Matchers, WordSpec}
 
 /**
  * @author Sergey Ionin
  */
 
-class TraitsTest extends WordSpec with Matchers {
-
-  import com.baeldung.scala.classcompositionwithtraits.CarTraits._
+class CarTraitsTest extends WordSpec with Matchers {
 
   "Class that extends Car" should {
     "inherit abstract class fields" in {
@@ -28,6 +27,14 @@ class TraitsTest extends WordSpec with Matchers {
     }
   }
 
+  "Classes that extends Car with SimpleMarshaller" should {
+    "inherit abstract class fields and methods" +
+      "and be marshallable" in {
+      val bmw0 = new BMW0("F15", 309) with SimpleMarshaller
+      bmw0.toJson shouldBe "{\"model\":F15,\n\"horsePower\":309}"
+    }
+  }
+
   "Classes that extends Car with Marshaller" should {
     "inherit abstract class fields and methods" +
       "and be marshallable" in {