Test for multiple namespaces

Add a test that verifies we don't do any moves when there are multiple
namespaces in the file.  There is no way to safely move a using in this
case using only syntax information.

This move effectively adds new namespaces at a global level which used
to be local to a namespace.  This means extension methods and types from
this namespace will affect compilation in all namespaces.  This can
introduce both compilation errors or even worse silently change overload
resolution in the file.

Author: jaredpar

src/Microsoft.DotNet.CodeFormatting.Tests/Rules/UsingLocationRuleTests.cs

@@ -36,6 +36,30 @@ class C1 { }
             Verify(source, expected);
         }
 
+        /// <summary>
+        /// There is no safe way to move a using outside a namespace when there are
+        /// multiple namespaces.  The rule should punt on this scenario. 
+        /// </summary>
+        [Fact]
+        public void SimpleMoveMultipleNamespaces()
+        {
+            var source = @"
+using NS1;
+namespace NS2
+{
+    using NS3;
+    class C1 { }
+}
+
+namespace NS3
+{
+    using NS4;
+    class C1 { }
+}";
+
+            Verify(source, source);
+        }
+
         [Fact]
         public void SimpleMoveWithComment()
         {