added Factory Method pattern and corresponding tests

src/main/kotlin/design_patterns/Abstract Factory.kt

@@ -5,7 +5,9 @@ import java.util.*
 /**
  *
  * An abstract factory is a generative design pattern that allows
+ *
  * you to create families of related objects without being tied to
+ *
  * the specific classes of objects you create.
  *
  */

src/main/kotlin/design_patterns/Factory Method.kt

@@ -0,0 +1,42 @@
+package design_patterns
+
+/**
+ *
+ * A factory method is a generic design pattern that defines
+ *
+ * a common interface for creating objects in a superclass,
+ *
+ * allowing subclasses to change the type of objects they create.
+ *
+ */
+
+abstract class Pony4
+
+class EarthPony4 : Pony4()
+class Pegasus4 : Pony4()
+class Unicorn4 : Pony4()
+
+abstract class Place {
+    private var numberOfPonies = 0
+
+    abstract fun pony() : Pony4
+
+    fun newPony() : Pony4 {
+        numberOfPonies++
+        return pony()
+    }
+
+    fun count() = numberOfPonies
+}
+
+class Cloudsdale : Place() {
+    override fun pony() = Pegasus4()
+}
+
+class Canterlot : Place() {
+    override fun pony() = Unicorn4()
+}
+
+class Ponyville : Place() {
+    override fun pony() = EarthPony4()
+}

src/test/kotlin/design_patterns/FactoryMethodTest.kt

@@ -0,0 +1,33 @@
+package design_patterns
+
+import org.hamcrest.MatcherAssert.assertThat
+import org.hamcrest.core.IsInstanceOf.instanceOf
+import org.junit.Test
+import org.junit.jupiter.api.Assertions.assertEquals
+
+class FactoryMethodTest {
+
+    @Test
+    fun test_match_objects() {
+        val ponyville = Ponyville()
+        val earthPony = ponyville.newPony()
+
+        assertThat(earthPony, instanceOf(EarthPony4::class.java))
+
+        val canterlot = Canterlot()
+        val unicorn = canterlot.newPony()
+
+        assertThat(unicorn, instanceOf(Unicorn4::class.java))
+    }
+
+    @Test
+    fun test_count() {
+        val cloudsDale = Cloudsdale()
+
+        cloudsDale.newPony()
+        cloudsDale.newPony()
+        cloudsDale.newPony()
+
+        assertEquals(3, cloudsDale.count())
+    }
+}