Added unit test as showcase

tests/NLog.UnitTests/Layouts/JsonLayoutTests.cs

@@ -31,6 +31,8 @@
 // THE POSSIBILITY OF SUCH DAMAGE.
 // 
 
+using NLog.Targets;
+
 namespace NLog.UnitTests.Layouts
 {
     using System;
@@ -192,7 +194,7 @@ public void NestedJsonAttrTest()
                     new JsonAttribute("message", "${exception:format=Message}"),
                     new JsonAttribute("innerException", new JsonLayout
                     {
-            
+
                         Attributes =
                         {
                             new JsonAttribute("type", "${exception:format=:innerFormat=Type:MaxInnerExceptionLevel=1:InnerExceptionSeparator=}"),
@@ -213,5 +215,59 @@ public void NestedJsonAttrTest()
             Assert.Equal("{ \"type\": \"NLog.NLogRuntimeException\", \"message\": \"test\", \"innerException\": { \"type\": \"System.NullReferenceException\", \"message\": \"null is bad!\" } }", json);
 
         }
+
+        [Fact]
+        public void NestedJsonAttrTestFromXML()
+        {
+            var configXml = @"
+<nlog>
+  <targets>
+    <target name='jsonFile' type='File' fileName='log.json'>
+      <layout type='JsonLayout'>
+        <attribute name='time' layout='${longdate}' />
+        <attribute name='level' layout='${level:upperCase=true}'/>
+        <attribute name='nested' encode='false'  >
+          <layout type='JsonLayout'>
+            <attribute name='message' layout='${message}' />
+            <attribute name='exception' layout='${exception}' />
+          </layout>
+        </attribute>
+      </layout>
+    </target>
+  </targets>
+  <rules>
+  </rules>
+</nlog>
+";
+
+            var config = CreateConfigurationFromString(configXml);
+
+            Assert.NotNull(config);
+            var target = config.FindTargetByName<FileTarget>("jsonFile");
+            Assert.NotNull(target);
+            var jsonLayout = target.Layout as JsonLayout;
+            Assert.NotNull(jsonLayout);
+            var attrs = jsonLayout.Attributes;
+            Assert.NotNull(attrs);
+            Assert.Equal(3, attrs.Count);
+            Assert.Equal(typeof(SimpleLayout), attrs[0].Layout.GetType());
+            Assert.Equal(typeof(SimpleLayout), attrs[1].Layout.GetType());
+            Assert.Equal(typeof(JsonLayout), attrs[2].Layout.GetType());
+            var nestedJsonLayout = (JsonLayout)attrs[2].Layout;
+            Assert.Equal(2, nestedJsonLayout.Attributes.Count);
+            Assert.Equal("'${message}'", nestedJsonLayout.Attributes[0].Layout.ToString());
+            Assert.Equal("'${exception}'", nestedJsonLayout.Attributes[1].Layout.ToString());
+
+            var logEventInfo = new LogEventInfo
+            {
+                TimeStamp = new DateTime(2016, 10, 30, 13, 30, 55),
+                Message = "this is message",
+                Level = LogLevel.Info,
+                Exception = new NLogRuntimeException("test", new NullReferenceException("null is bad!"))
+            };
+
+            var json = jsonLayout.Render(logEventInfo);
+            Assert.Equal("{ \"time\": \"2016-10-30 13:30:55.0000\", \"level\": \"INFO\", \"nested\": { \"message\": \"this is message\", \"exception\": \"test\" } }", json);
+        }
     }
 }