Add tests around new 'add null check' behavior.

src/EditorFeatures/CSharpTest/GenerateFromMembers/GenerateConstructorFromMembers/GenerateConstructorFromMembersTests.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.Collections.Immutable;
 using System.Threading.Tasks;
 using Microsoft.CodeAnalysis.CodeRefactorings;
 using Microsoft.CodeAnalysis.CodeStyle;
 using Microsoft.CodeAnalysis.CSharp.CodeStyle;
-using Microsoft.CodeAnalysis.CSharp.Test.Utilities;
 using Microsoft.CodeAnalysis.Editor.CSharp.UnitTests.CodeRefactorings;
 using Microsoft.CodeAnalysis.GenerateConstructorFromMembers;
 using Microsoft.CodeAnalysis.PickMembers;
@@ -729,6 +727,79 @@ public Z(string b, int a)
 chosenSymbols: new string[] { "b", "a" });
         }
 
+        [Fact, Trait(Traits.Feature, Traits.Features.CodeActionsGenerateConstructorFromMembers)]
+        public async Task TestAddNullChecks1()
+        {
+            await TestWithPickMembersDialogAsync(
+@"
+using System;
+using System.Collections.Generic;
+
+class Z
+{
+    int a;
+    string b;
+    [||]
+}",
+@"
+using System;
+using System.Collections.Generic;
+
+class Z
+{
+    int a;
+    string b;
+
+    public Z(int a, string b)
+    {
+        this.a = a;
+        this.b = b ?? throw new ArgumentNullException(nameof(b));
+    }
+}",
+chosenSymbols: new string[] { "a", "b" }, 
+optionsCallback: options => options[0].Value = true);
+        }
+
+        [Fact, Trait(Traits.Feature, Traits.Features.CodeActionsGenerateConstructorFromMembers)]
+        public async Task TestAddNullChecks2()
+        {
+            await TestWithPickMembersDialogAsync(
+@"
+using System;
+using System.Collections.Generic;
+
+class Z
+{
+    int a;
+    string b;
+    [||]
+}",
+@"
+using System;
+using System.Collections.Generic;
+
+class Z
+{
+    int a;
+    string b;
+
+    public Z(int a, string b)
+    {
+        if (b == null)
+        {
+            throw new ArgumentNullException(nameof(b));
+        }
+
+        this.a = a;
+        this.b = b;
+    }
+}",
+chosenSymbols: new string[] { "a", "b" },
+optionsCallback: options => options[0].Value = true,
+parameters: new TestParameters(options:
+    Option(CodeStyleOptions.PreferThrowExpression, CodeStyleOptions.FalseWithNoneEnforcement)));
+        }
+
         [Fact, Trait(Traits.Feature, Traits.Features.CodeActionsGenerateConstructorFromMembers)]
         public async Task TestMissingOnMember1()
         {

src/EditorFeatures/TestUtilities/CodeActions/AbstractCodeActionTest.cs

@@ -113,21 +113,26 @@ public abstract class AbstractCodeActionTest : AbstractCodeActionOrUserDiagnosti
         }
 
         protected static Document GetDocument(TestWorkspace workspace)
-        {
-            return workspace.CurrentSolution.GetDocument(workspace.Documents.First().Id);
-        }
+            => workspace.CurrentSolution.GetDocument(workspace.Documents.First().Id);
 
         private class TestPickMembersService : IPickMembersService
         {
             private readonly ImmutableArray<string> _memberNames;
+            private readonly Action<ImmutableArray<PickMembersOption>> _optionsCallback;
 
-            public TestPickMembersService(ImmutableArray<string> memberNames)
-                => _memberNames = memberNames;
+            public TestPickMembersService(
+                ImmutableArray<string> memberNames,
+                Action<ImmutableArray<PickMembersOption>> optionsCallback)
+            {
+                _memberNames = memberNames;
+                _optionsCallback = optionsCallback;
+            }
 
             public PickMembersResult PickMembers(
                 string title, ImmutableArray<ISymbol> members,
                 ImmutableArray<PickMembersOption> options)
             {
+                _optionsCallback?.Invoke(options);
                 return new PickMembersResult(
                     _memberNames.IsDefault
                         ? members
@@ -140,12 +145,13 @@ public TestPickMembersService(ImmutableArray<string> memberNames)
             string initialMarkup,
             string expectedMarkup,
             string[] chosenSymbols,
+            Action<ImmutableArray<PickMembersOption>> optionsCallback = null,
             int index = 0,
             bool ignoreTrivia = true,
             CodeActionPriority? priority = null,
             TestParameters parameters = default(TestParameters))
         {
-            var pickMembersService = new TestPickMembersService(chosenSymbols.AsImmutableOrNull());
+            var pickMembersService = new TestPickMembersService(chosenSymbols.AsImmutableOrNull(), optionsCallback);
             return TestInRegularAndScript1Async(
                 initialMarkup, expectedMarkup,
                 index, ignoreTrivia, priority,