[tdd-diamond] Letter is enum

tdd-diamond/src/main/java/com/michaelszymczak/diamond/Diamond.java

@@ -2,17 +2,17 @@
 
 public class Diamond {
 
-  private char letter;
+  private Letter letter;
 
-  public static Diamond of(char letter) {
+  public static Diamond of(Letter letter) {
     return new Diamond(letter);
   }
 
-  private Diamond(char letter) {
+  private Diamond(Letter letter) {
     this.letter = letter;
   }
 
   public String rendered() {
-    return letter == 'A' ? "A" : " A \nB B\n A ";
+    return letter == Letter.A ? "A" : " A \nB B\n A ";
   }
 }

tdd-diamond/src/main/java/com/michaelszymczak/diamond/Letter.java

@@ -0,0 +1,5 @@
+package com.michaelszymczak.diamond;
+
+public enum Letter {
+  A, B
+}

tdd-diamond/src/test/groovy/com/michaelszymczak/diamond/DiamondAcceptanceTest.groovy

@@ -6,14 +6,14 @@ class DiamondAcceptanceTest extends Specification {
 
   def "contains one letter if it is the first letter"() {
     expect:
-    Diamond.of('A' as char).rendered() == "A"
+    Diamond.of(Letter.A).rendered() == "A"
   }
 
   def "creates diamond shape if more than one letter"() {
     expect:
-    Diamond.of('B' as char).rendered() == " A " + "\n" +
-                                          "B B" + "\n" +
-                                          " A "
-
+    Diamond.of(Letter.B).rendered() == "" +
+            " A " + "\n" +
+            "B B" + "\n" +
+            " A "
   }
 }