Updated test cases documentation

docs/test_cases/t00018.md

@@ -16,34 +16,13 @@ diagrams:
 
 ```
 ## Source code
-File t00018_impl.h
-```cpp
-#pragma once
-
-#include "t00018.h"
-
-namespace clanguml {
-namespace t00018 {
-namespace impl {
-
-class widget {
-    int n;
-
-public:
-    void draw(const clanguml::t00018::widget &w) const;
-    void draw(const clanguml::t00018::widget &w);
-    widget(int n);
-};
-}
-}
-}
-
-```
 File t00018.h
 ```cpp
 #pragma once
 
+#ifndef _MSC_VER
 #include <experimental/propagate_const>
+#endif
 #include <iostream>
 #include <memory>
 
@@ -74,6 +53,29 @@ public:
 }
 }
 
+```
+File t00018_impl.h
+```cpp
+#pragma once
+
+#include "t00018.h"
+
+namespace clanguml {
+namespace t00018 {
+namespace impl {
+
+class widget {
+    int n;
+
+public:
+    void draw(const clanguml::t00018::widget &w) const;
+    void draw(const clanguml::t00018::widget &w);
+    widget(int n);
+};
+}
+}
+}
+
 ```
 File t00018.cc
 ```cpp