NSString: Use SecurityElement.Escape to escape XML characters

plist-cil.test/NSStringTests.cs

@@ -0,0 +1,29 @@
+using Claunia.PropertyList;
+using Xunit;
+
+namespace plistcil.test
+{
+    public class NSStringTests
+    {
+        const string START_TOKEN = "<string>";
+        const string END_TOKEN = "</string>";
+
+        [InlineData("abc", "abc")]
+        [InlineData("a>b", "a&gt;b")]
+        [InlineData("a<b", "a&lt;b")]
+        [InlineData("a&b", "a&amp;b")]
+        [Theory]
+        public void Content_IsEscaped(string value, string content)
+        {
+            var element = new NSString(value);
+            string xml = element.ToXmlPropertyList();
+
+            // Strip the leading and trailing data, so we just get the string element itself
+            int start = xml.IndexOf(START_TOKEN) + START_TOKEN.Length;
+            int end = xml.IndexOf(END_TOKEN);
+            string actualContent = xml.Substring(start, end - start);
+
+            Assert.Equal(content, actualContent);
+        }
+    }
+}