Just a commit

kotlin/hello-world/src/main/kotlin/HelloWorld.kt

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+/**
+ * Simple HelloWorld singleton class as defined by the `Kotlin object keyword`.
+ * See: https://kotlinlang.org/docs/reference/object-declarations.html#object-declarations
+ *
+ * As an alternative one could create a class such as:
+ * ```
+ * class HelloWorld(name: String? = "Default Value") {
+ *     fun hello(): String {
+ *
+ *     }
+ * }
+ * ```
+ * Resulting in a call such as: `HelloWorld("Bob").hello()`
+ * See: https://kotlinlang.org/docs/reference/classes.html#constructors
+ *
+ * In Kotlin we make objects defined as nullable via the trailing `?`, if you try
+ * to assign a null value to any value that isn't nullable a compilation error is thrown.
+ * Kotlin makes sure you are accessing nullable values safely and provides null safe calls
+ * and the use of the elvis operator. See: https://kotlinlang.org/docs/reference/null-safety.html
+ *
+ * You may provide default values on methods, so if an argument is omitted the default is used.
+ * See: https://kotlinlang.org/docs/reference/functions.html#default-arguments
+ *
+ * Kotlin provides String interpolation to make String formatting simple.
+ * See: https://kotlinlang.org/docs/reference/idioms.html#string-interpolation
+ */
+object HelloWorld {
+    fun hello(name: String? = "Default Argument"): String {
+
+    }
+}

kotlin/hello-world/src/test/kotlin/HelloWorldTest.kt

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+import kotlin.test.assertEquals
+import org.junit.Test
+
+class HelloWorldTest {
+
+    @Test
+    fun helloNoName() {
+        assertEquals("Hello, World!", HelloWorld.hello())
+    }
+
+    @Test
+    fun helloBlankName() {
+        assertEquals("Hello, World!", HelloWorld.hello(""))
+        assertEquals("Hello, World!", HelloWorld.hello("    "))
+    }
+
+    @Test
+    fun helloNullName() {
+        //This isn't advised in Kotlin but demonstrates the null safety in Kotlin
+        assertEquals("Hello, World!", HelloWorld.hello(null))
+    }
+
+    @Test
+    fun helloSampleName() {
+        assertEquals("Hello, Alice!", HelloWorld.hello("Alice"))
+    }
+
+    @Test
+    fun helloAnotherSampleName() {
+        assertEquals("Hello, Bob!", HelloWorld.hello("Bob"))
+    }
+}