Removed duplicated test helper

src/Workspaces/CoreTestUtilities/WorkspaceTestBase.cs

@@ -225,25 +225,6 @@ protected static string GetParentDirOfParentDirOfContainingDir(string fileName)
             return Directory.GetParent(parentOfContainingDir).FullName;
         }
 
-        protected static void AssertThrows<TException>(Action action, Action<TException> checker = null)
-            where TException : Exception
-        {
-            try
-            {
-                action();
-            }
-            catch (Exception e)
-            {
-                if (e is AggregateException agg && agg.InnerExceptions.Count == 1)
-                {
-                    e = agg.InnerExceptions[0];
-                }
-
-                Assert.Equal(typeof(TException), e.GetType());
-                checker?.Invoke((TException)e);
-            }
-        }
-
         protected int GetMethodInsertionPoint(VB.Syntax.ClassBlockSyntax cb)
         {
             if (cb.Implements.Count > 0)

src/Workspaces/MSBuildTest/MSBuildWorkspaceTests.cs

@@ -19,7 +19,6 @@
 using Roslyn.Test.Utilities;
 using Roslyn.Utilities;
 using Xunit;
-using Xunit.Abstractions;
 using static Microsoft.CodeAnalysis.MSBuild.UnitTests.SolutionGeneration;
 using CS = Microsoft.CodeAnalysis.CSharp;
 using VB = Microsoft.CodeAnalysis.VisualBasic;
@@ -2887,7 +2886,7 @@ public void TestOpenProject_WithProjectFileLocked()
             var projectFile = GetSolutionFileName(@"CSharpProject\CSharpProject.csproj");
             using (File.Open(projectFile, FileMode.Open, FileAccess.ReadWrite))
             {
-                AssertThrows<IOException>(() =>
+                AssertEx.Throws<IOException>(() =>
                     {
                         using (var workspace = CreateMSBuildWorkspace())
                         {
@@ -2904,7 +2903,7 @@ public void TestOpenProject_WithNonExistentProjectFile()
 
             // open for read-write so no-one else can read
             var projectFile = GetSolutionFileName(@"CSharpProject\NoProject.csproj");
-            AssertThrows<FileNotFoundException>(() =>
+            AssertEx.Throws<FileNotFoundException>(() =>
                 {
                     using (var workspace = CreateMSBuildWorkspace())
                     {
@@ -2920,7 +2919,7 @@ public void TestOpenSolution_WithNonExistentSolutionFile()
 
             // open for read-write so no-one else can read
             var solutionFile = GetSolutionFileName(@"NoSolution.sln");
-            AssertThrows<System.IO.FileNotFoundException>(() =>
+            AssertEx.Throws<FileNotFoundException>(() =>
                 {
                     using (var workspace = CreateMSBuildWorkspace())
                     {