Fix bug in fetch and add unit tests.

lib/tainted_hash.rb

@@ -90,14 +90,16 @@ class TaintedHash < Hash
   #
   # Returns the value of the key, or the default.
   def fetch(key, *default)
+    raise ArgumentError, "wrong number of arguments (#{default.size + 1} for 1..2)" if default.size > 1
+
     key_s = key.to_s
     if @original_hash.key?(key_s)
       self[key_s]
     elsif block_given?
       yield
-    elsif default
+    elsif !default.empty?
       default[0]
-    else
+    elsif
       raise KeyError, "key not found: #{key}"
     end
   end

test/tainted_hash_test.rb

@@ -74,6 +74,10 @@ class TaintedHashTest < Test::Unit::TestCase
     assert !@tainted.include?(:d)
     assert_equal 1, @tainted.fetch(:a, :default)
     assert_equal :default, @tainted.fetch(:d, :default)
+    assert_raises KeyError do
+      @tainted.fetch(:d)
+    end
+    assert_equal :default, @tainted.fetch(:d) { :default }
     assert !@tainted.include?(:a)
     assert !@tainted.include?(:d)
   end