Convert the type inferrer tests to be Theories

Most of the type inferrer tests test both overloads of the
type inferrence service -- the one that takes a span and one that
takes a position. Both (by default) were tested, but it's impossible
without actually debugging a test to know which one failed. I had a
particular irritating case where I made a behavior change and had to
update a bunch of tests with new baselines, but since the behavior
also split between both APIs it was confusing to figure out what was
going on.

src/EditorFeatures/CSharpTest/Microsoft.CodeAnalysis.CSharp.EditorFeatures.UnitTests.csproj

@@ -66,6 +66,7 @@
     <PackageReference Include="Microsoft.VisualStudio.Text.UI.Wpf" Version="$(MicrosoftVisualStudioTextUIWpfVersion)" />
     <PackageReference Include="Microsoft.VisualStudio.Utilities" Version="$(MicrosoftVisualStudioUtilitiesVersion)" />
     <PackageReference Include="Microsoft.VisualStudio.Validation" Version="$(MicrosoftVisualStudioValidationVersion)" />
+    <PackageReference Include="Xunit.Combinatorial" Version="$(XunitCombinatorialVersion)" PrivateAssets="all" />
   </ItemGroup>
   <ItemGroup>
     <Service Include="{82A7F48D-3B50-4B1E-B82E-3ADA8210C358}" />

src/EditorFeatures/TestUtilities/TypeInferrer/TypeInferrerTestBase.cs

@@ -37,39 +37,37 @@ private static async Task<bool> CanUseSpeculativeSemanticModelAsync(Document doc
             return !service.GetMemberBodySpanForSpeculativeBinding(node).IsEmpty;
         }
 
-        protected async Task TestAsync(string text, string expectedType, bool testNode = true, bool testPosition = true,
-            SourceCodeKind sourceCodeKind = SourceCodeKind.Regular)
+        /// <summary>
+        /// Specifies which overload of the <see cref="ITypeInferenceService"/> will be tested.
+        /// </summary>
+        public enum TestMode
         {
-            MarkupTestFile.GetSpan(text.NormalizeLineEndings(), out text, out var textSpan);
-
-            if (testNode)
-            {
-                await TestWithAndWithoutSpeculativeSemanticModelAsync(text, textSpan, expectedType, useNodeStartPosition: false, sourceCodeKind);
-            }
+            /// <summary>
+            /// Specifies the test is going to call into <see cref="ITypeInferenceService.InferTypes(SemanticModel, SyntaxNode, string, System.Threading.CancellationToken)"/>.
+            /// </summary>
+            Node,
 
-            if (testPosition)
-            {
-                await TestWithAndWithoutSpeculativeSemanticModelAsync(text, textSpan, expectedType, useNodeStartPosition: true, sourceCodeKind);
-            }
+            /// <summary>
+            /// Specifies the test is going to call into <see cref="ITypeInferenceService.InferTypes(SemanticModel, int, string, System.Threading.CancellationToken)"/>.
+            /// </summary>
+            Position
         }
 
-        private async Task TestWithAndWithoutSpeculativeSemanticModelAsync(
-            string text,
-            TextSpan textSpan,
-            string expectedType,
-            bool useNodeStartPosition,
-            SourceCodeKind sourceCodeKind)
+        protected async Task TestAsync(string text, string expectedType, TestMode mode,
+            SourceCodeKind sourceCodeKind = SourceCodeKind.Regular)
         {
+            MarkupTestFile.GetSpan(text.NormalizeLineEndings(), out text, out var textSpan);
+
             var document = fixture.UpdateDocument(text, sourceCodeKind);
-            await TestWorkerAsync(document, textSpan, expectedType, useNodeStartPosition);
+            await TestWorkerAsync(document, textSpan, expectedType, mode);
 
             if (await CanUseSpeculativeSemanticModelAsync(document, textSpan.Start))
             {
                 var document2 = fixture.UpdateDocument(text, sourceCodeKind, cleanBeforeUpdate: false);
-                await TestWorkerAsync(document2, textSpan, expectedType, useNodeStartPosition);
+                await TestWorkerAsync(document2, textSpan, expectedType, mode);
             }
         }
 
-        protected abstract Task TestWorkerAsync(Document document, TextSpan textSpan, string expectedType, bool useNodeStartPosition);
+        protected abstract Task TestWorkerAsync(Document document, TextSpan textSpan, string expectedType, TestMode mode);
     }
 }

src/EditorFeatures/VisualBasicTest/Microsoft.CodeAnalysis.VisualBasic.EditorFeatures.UnitTests.vbproj

@@ -59,6 +59,7 @@
     <PackageReference Include="Microsoft.VisualStudio.Text.UI.Wpf" Version="$(MicrosoftVisualStudioTextUIWpfVersion)" />
     <PackageReference Include="Microsoft.VisualStudio.Utilities" Version="$(MicrosoftVisualStudioUtilitiesVersion)" />
     <PackageReference Include="Microsoft.VisualStudio.Validation" Version="$(MicrosoftVisualStudioValidationVersion)" />
+    <PackageReference Include="Xunit.Combinatorial" Version="$(XunitCombinatorialVersion)" PrivateAssets="all" />
   </ItemGroup>
   <ItemGroup>
     <Import Include="Microsoft.CodeAnalysis.Editor.Shared.Extensions" />