Tests for preprocessor directives

This adds tests for how we handle preprocessor directives with respect
to file formatting.

closes #38

Author: jaredpar

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

@@ -26,6 +26,7 @@ public CombinationTest()
         {
             s_formattingEngine.CopyrightHeader = ImmutableArray.Create("", "// header");
             s_formattingEngine.FormatLogger = new EmptyFormatLogger();
+            s_formattingEngine.PreprocessorConfigurations = ImmutableArray<string[]>.Empty;
         }
 
         protected override async Task<Document> RewriteDocumentAsync(Document document)
@@ -93,5 +94,57 @@ private void M()
 
             Verify(text, expected, runFormatter: false);
         }
+
+        [Fact]
+        public void PreprocessorSymbolNotDefined()
+        {
+            var text = @"
+class C
+{
+#if DOG
+    void M() { } 
+#endif 
+}";
+
+            var expected = @"
+// header
+
+internal class C
+{
+#if DOG
+    void M() { } 
+#endif 
+}";
+
+            Verify(text, expected, runFormatter: false);
+        }
+
+        [Fact]
+        public void PreprocessorSymbolDefined()
+        {
+            var text = @"
+internal class C
+{
+#if DOG
+    internal void M() {
+} 
+#endif 
+}";
+
+            var expected = @"
+// header
+
+internal class C
+{
+#if DOG
+    internal void M()
+    {
+    }
+#endif
+}";
+
+            s_formattingEngine.PreprocessorConfigurations = ImmutableArray.CreateRange(new[] { new[] { "DOG" } });
+            Verify(text, expected, runFormatter: false);
+        }
     }
 }