Add C# tests.

src/EditorFeatures/CSharpTest/CSharpEditorServicesTest.csproj

@@ -93,8 +93,10 @@
     <AssemblyName>Roslyn.Services.Editor.CSharp.UnitTests</AssemblyName>
     <RoslynProjectType>UnitTest</RoslynProjectType>
   </PropertyGroup>
-  <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' "></PropertyGroup>
-  <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Release|AnyCPU' "></PropertyGroup>
+  <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
+  </PropertyGroup>
+  <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Release|AnyCPU' ">
+  </PropertyGroup>
   <ItemGroup>
     <Reference Include="Microsoft.CSharp" />
     <Reference Include="PresentationCore" />
@@ -278,6 +280,7 @@
     <Compile Include="Formatting\Indentation\SmartTokenFormatterFormatTokenTests.cs" />
     <Compile Include="InlineDeclaration\CSharpInlineDeclarationTests_FixAllTests.cs" />
     <Compile Include="InlineDeclaration\CSharpInlineDeclarationTests.cs" />
+    <Compile Include="UseCoalesceExpression\UseCoalesceExpressionTests.cs" />
     <Compile Include="UsePatternMatching\CSharpIsAndCastCheckTests_FixAllTests.cs" />
     <Compile Include="UsePatternMatching\CSharpIsAndCastCheckTests.cs" />
     <Compile Include="UsePatternMatching\CSharpAsAndNullCheckTests.cs" />

src/EditorFeatures/CSharpTest/UseCoalesceExpression/UseCoalesceExpressionTests.cs

+// Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using Microsoft.CodeAnalysis.CodeFixes;
+using Microsoft.CodeAnalysis.CSharp.UseCoalesceExpression;
+using Microsoft.CodeAnalysis.Diagnostics;
+using Microsoft.CodeAnalysis.Editor.CSharp.UnitTests.Diagnostics;
+using Microsoft.CodeAnalysis.UseCoalesceExpression;
+using Roslyn.Test.Utilities;
+using Xunit;
+
+namespace Microsoft.CodeAnalysis.Editor.CSharp.UnitTests.UseCoalesceExpression
+{
+    public class UseCoalesceExpressionTests : AbstractCSharpDiagnosticProviderBasedUserDiagnosticTest
+    {
+        internal override Tuple<DiagnosticAnalyzer, CodeFixProvider> CreateDiagnosticProviderAndFixer(Workspace workspace)
+        {
+            return new Tuple<DiagnosticAnalyzer, CodeFixProvider>(
+                new CSharpUseCoalesceExpressionDiagnosticAnalyzer(),
+                new UseCoalesceExpressionCodeFixProvider());
+        }
+
+        [Fact, Trait(Traits.Feature, Traits.Features.CodeActionsUseCoalesceExpression)]
+        public async Task TestOnLeft_Equals()
+        {
+            await TestAsync(
+@"
+using System;
+
+class C
+{
+    void M(string x, string y)
+    {
+        var z = [||]x == null ? y : x;
+    }
+}",
+@"using System;
+
+class C
+{
+    void M(string x, string y)
+    {
+        var z = x ?? y;
+    }
+}");
+        }
+
+        [Fact, Trait(Traits.Feature, Traits.Features.CodeActionsUseCoalesceExpression)]
+        public async Task TestOnLeft_NotEquals()
+        {
+            await TestAsync(
+@"
+using System;
+
+class C
+{
+    void M(string x, string y)
+    {
+        var z = [||]x != null ? x : y;
+    }
+}",
+@"using System;
+
+class C
+{
+    void M(string x, string y)
+    {
+        var z = x ?? y;
+    }
+}");
+        }
+
+        [Fact, Trait(Traits.Feature, Traits.Features.CodeActionsUseCoalesceExpression)]
+        public async Task TestOnRight_Equals()
+        {
+            await TestAsync(
+@"
+using System;
+
+class C
+{
+    void M(string x, string y)
+    {
+        var z = [||]null == x ? y : x;
+    }
+}",
+@"using System;
+
+class C
+{
+    void M(string x, string y)
+    {
+        var z = x ?? y;
+    }
+}");
+        }
+
+        [Fact, Trait(Traits.Feature, Traits.Features.CodeActionsUseCoalesceExpression)]
+        public async Task TestOnRight_NotEquals()
+        {
+            await TestAsync(
+@"
+using System;
+
+class C
+{
+    void M(string x, string y)
+    {
+        var z = [||]null != x ? x : y;
+    }
+}",
+@"using System;
+
+class C
+{
+    void M(string x, string y)
+    {
+        var z = x ?? y;
+    }
+}");
+        }
+
+        [Fact, Trait(Traits.Feature, Traits.Features.CodeActionsUseCoalesceExpression)]
+        public async Task TestComplexExpression()
+        {
+            await TestAsync(
+@"
+using System;
+
+class C
+{
+    void M(string x, string y)
+    {
+        var z = [||]x.ToString() == null ? y : x.ToString();
+    }
+}",
+@"using System;
+
+class C
+{
+    void M(string x, string y)
+    {
+        var z = x.ToString() ?? y;
+    }
+}");
+        }
+    }
+}
\ No newline at end of file

src/EditorFeatures/TestUtilities/Traits.cs

@@ -84,6 +84,7 @@ public static class Features
             public const string CodeActionsSpellcheck = "CodeActions.Spellcheck";
             public const string CodeActionsSuppression = "CodeActions.Suppression";
             public const string CodeActionsUseAutoProperty = "CodeActions.UseAutoProperty";
+            public const string CodeActionsUseCoalesceExpression = "CodeActions.UseCoalesceExpression";
             public const string CodeActionsUseExpressionBody = "CodeActions.UseExpressionBody";
             public const string CodeActionsUseImplicitType = "CodeActions.UseImplicitType";
             public const string CodeActionsUseExplicitType = "CodeActions.UseExplicitType";