Adds additional test for two-fer exercise

exercises/two-fer/src/test/java/TwoferTest.java

@@ -38,4 +38,13 @@ public class TwoferTest {
 
         assertEquals(expected, twofer.twofer(input));
     }
+
+    @Ignore("Remove to run test")
+    @Test
+    public void emptyStringGiven() {
+        String input = "";
+        String expected = "One for , one for me.";
+
+        assertEquals(expected, twofer.twofer(input) );
+    }
 }