Stack top and pop return nil if stack is empty

pmatsinopoulos · Feb 12, 2012 · c2e0776 · c2e0776
1 parent 5465485
commit c2e0776
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Showing 2 changed files with 12 additions and 0 deletions.
diff --git a/models/stack.rb b/models/stack.rb
@@ -10,10 +10,12 @@ def push(element)
   end
 
   def pop
+    return nil if empty?
     @stack.delete_at(@stack.size - 1)
   end
 
   def top
+    return nil if empty?
     @stack[@stack.size - 1]
   end
 

diff --git a/test/unit/stack_test.rb b/test/unit/stack_test.rb
@@ -25,6 +25,11 @@ def test_pop
     assert_equal number_of_elements_after - 1, @stack.size
   end
 
+  def test_pop_returns_nil_on_empty_stack
+    s = Stack.new
+    assert_nil s.pop
+  end
+
   def test_top
     number_of_elements_before = @stack.size
     @stack.push(1)
@@ -33,6 +38,11 @@ def test_top
     assert_equal 1, @stack.top
   end
 
+  def test_top_returns_nil_on_empty_stack
+    s = Stack.new
+    assert_nil s.top
+  end
+
   def test_size
     assert @stack.empty?
     @stack.push(1)