Ensure double quotes are not escaped twice

lib/masamune/schema/map.rb

@@ -44,7 +44,11 @@ def skip?
       end
 
       def encode(fields = [])
-        fields.map { |field| field =~ /^{|}$/ ? %Q{"#{field.gsub('"', '""')}"} : field }
+        fields.map { |field| field =~ /^{|}$/ ? quote(field) : field }
+      end
+
+      def quote(field)
+        %Q{"#{field.gsub(/(?<!")"(?!")/, '""')}"}
       end
 
       def separator

spec/masamune/schema/map_spec.rb

@@ -530,4 +530,36 @@
       it_behaves_like 'apply input/output'
     end
   end
+
+  describe Masamune::Schema::Map::JSONEncoder do
+    let(:io) { StringIO.new }
+    let(:store) { double(json_encoding: :raw, format: :csv) }
+    let(:encoder) { described_class.new(io, store) }
+
+    subject { encoder.gets }
+
+    context 'with raw json' do
+      before do
+        io.write '{"enabled":true}'
+        io.rewind
+      end
+      it { is_expected.to eq(%Q{"{""enabled"":true}"}) }
+    end
+
+    context 'with quoted json' do
+      before do
+        io.write '"{""enabled"":true}"'
+        io.rewind
+      end
+      it { is_expected.to eq(%Q{"{""enabled"":true}"}) }
+    end
+
+    context 'with partially quoted json' do
+      before do
+        io.write '{""enabled"":true}'
+        io.rewind
+      end
+      it { is_expected.to eq(%Q{"{""enabled"":true}"}) }
+    end
+  end
 end