fix to_s

lib/register/instructions/branch.rb

@@ -10,7 +10,7 @@ module Register
     attr_reader :label
 
     def to_s
-      "#{self.class.name}: #{label.name}"
+      "#{self.class.name}: #{label ? label.name : ''}"
     end
     alias :inspect :to_s
 

test/register/test_instructions.rb

@@ -7,6 +7,20 @@ module Register
       @branch = Branch.new(nil , @label)
       @instruction = Instruction.new(nil)
     end
+    def test_branch_tos1
+      assert @branch.to_s.include?("Branch")
+      assert @branch.to_s.include?("test")
+    end
+    def test_branch_tos2
+      branch = Branch.new(nil ,nil)
+      assert branch.to_s.include?("Branch")
+    end
+    def test_label_tos1
+      assert @label.to_s.include?("Label")
+    end
+    def test_label_tos2
+      assert Label.new(nil,nil).to_s.include?("Label")
+    end
     def test_last_empty
       assert_equal @instruction, @instruction.last
     end