diff --git a/src/libraries/Common/tests/System/Xml/ModuleCore/ctestexception.cs b/src/libraries/Common/tests/System/Xml/ModuleCore/ctestexception.cs
index 60a033f7853f..0467c7b4d574 100644
--- a/src/libraries/Common/tests/System/Xml/ModuleCore/ctestexception.cs
+++ b/src/libraries/Common/tests/System/Xml/ModuleCore/ctestexception.cs
@@ -58,24 +58,24 @@ public class CTestException : Exception
         public object Expected;
 
         //Constructor
-        public CTestException(string message)
+        public CTestException(string message!!)
             : this(CTestBase.TEST_FAIL, message)
         {
         }
 
-        public CTestException(int result, string message)
+        public CTestException(int result, string message!!)
             : this(result, message, false, true, null)
         {
         }
 
-        public CTestException(int result, string message, object actual, object expected, Exception inner)
+        public CTestException(int result, string message!!, object actual, object expected, Exception inner)
             : base(message, inner)
         {
             //Note: iResult is the variation result (i.e.: TEST_PASS, TEST_FAIL, etc...)
             //Setup the exception
             Result = result;
-            Actual = actual;
-            Expected = expected;
+            Actual = actual ?? "";
+            Expected = expected ?? "";
         }
 
         public override string Message
diff --git a/src/libraries/Common/tests/System/Xml/XmlCoreTest/CustomWriter.cs b/src/libraries/Common/tests/System/Xml/XmlCoreTest/CustomWriter.cs
index 7ead330b9f6d..1c06afbda82f 100644
--- a/src/libraries/Common/tests/System/Xml/XmlCoreTest/CustomWriter.cs
+++ b/src/libraries/Common/tests/System/Xml/XmlCoreTest/CustomWriter.cs
@@ -157,6 +157,11 @@ public override string XmlLang
             }
         }
 
+        public override void Close()
+        {
+            Dispose(disposing:true);
+        }
+
         protected override void Dispose(bool disposing)
         {
             if (disposing)
diff --git a/src/libraries/Common/tests/System/Xml/XmlCoreTest/FilePathUtil.cs b/src/libraries/Common/tests/System/Xml/XmlCoreTest/FilePathUtil.cs
index 4524d11ceab4..b5a64db4aab0 100644
--- a/src/libraries/Common/tests/System/Xml/XmlCoreTest/FilePathUtil.cs
+++ b/src/libraries/Common/tests/System/Xml/XmlCoreTest/FilePathUtil.cs
@@ -111,8 +111,7 @@ public static string ExpandVariables(string inputPath)
             return resultPath.ToString();
         }
 
-        private static MyDict<string, Stream> s_XmlFileInMemoryCache = null;
-        private static MyDict<string, Stream> s_XmlFileInMemoryCacheBackup = null;
+        private static MyDict<string, MemoryStream> s_XmlFileInMemoryCache = null;
 
         private static readonly object s_XmlFileMemoryCacheLock = new object();
         static void initXmlFileCacheIfNotYet()
@@ -121,35 +120,20 @@ static void initXmlFileCacheIfNotYet()
             {
                 if (s_XmlFileInMemoryCache == null)
                 {
-                    s_XmlFileInMemoryCache = new MyDict<string, Stream>();
-                    s_XmlFileInMemoryCacheBackup = new MyDict<string, Stream>();
+                    s_XmlFileInMemoryCache = new MyDict<string, MemoryStream>();
 
-                    foreach (var file in GetDataFiles())
+                    foreach (Tuple<string, byte[]> file in GetDataFiles())
                     {
-                        addBytes(file.Item1, file.Item2);
+                        var ms = new MemoryStream(file.Item2);
+                        s_XmlFileInMemoryCache[NormalizeFilePath(file.Item1)] = ms;
                     }
                 }
             }
         }
 
-        public static void cacheXml(string filename, string content)
-        {
-            initXmlFileCacheIfNotYet();
-            MemoryStream ms = new MemoryStream();
-            StreamWriter sw = new StreamWriter(ms);
-            sw.Write(content);
-            sw.Flush();
-            s_XmlFileInMemoryCache[NormalizeFilePath(filename)] = ms;
-
-            MemoryStream msbak = new MemoryStream();
-            ms.Position = 0;
-            ms.CopyTo(msbak);
-            s_XmlFileInMemoryCacheBackup[NormalizeFilePath(filename)] = msbak;
-        }
-
         public static Stream getStreamDirect(string filename)
         {
-            foreach (var file in GetDataFiles())
+            foreach (Tuple<string, byte[]> file in GetDataFiles())
             {
                 if (file.Item1 == filename)
                 {
@@ -171,51 +155,23 @@ public static Stream getStream(string filename)
 
             lock (s_XmlFileMemoryCacheLock)
             {
-                Stream s = s_XmlFileInMemoryCache[normalizedFileName];
+                MemoryStream ms = s_XmlFileInMemoryCache[normalizedFileName];
 
-                if (s == null)
+                if (ms == null)
                 {
                     throw new FileNotFoundException("File Not Found: " + filename);
                 }
 
-                if (s.CanSeek)
-                {
-                    s.Position = 0;
-                    return s;
-                }
-                else
-                {
-                    Stream msbak = s_XmlFileInMemoryCacheBackup[normalizedFileName];
-                    MemoryStream msnew = new MemoryStream();
-                    msbak.Position = 0;
-                    msbak.CopyTo(msnew);
-
-                    s_XmlFileInMemoryCache[normalizedFileName] = msnew;
-                    msnew.Position = 0;
-                    return msnew;
-                }
-            }
-        }
-
-        public static void addBytes(string filename, byte[] bytes)
-        {
-            if (null == filename)
-                return;
-
-            initXmlFileCacheIfNotYet();
-
-            lock (s_XmlFileMemoryCacheLock)
-            {
-                var ms = new MemoryStream(bytes);
-                s_XmlFileInMemoryCache[NormalizeFilePath(filename)] = ms;
-                MemoryStream msbak = new MemoryStream();
+                // Always give out a new stream, so there's no concern about concurrent use
+                MemoryStream msnew = new MemoryStream();
                 ms.Position = 0;
-                ms.CopyTo(msbak);
-                s_XmlFileInMemoryCacheBackup[NormalizeFilePath(filename)] = msbak;
+                ms.CopyTo(msnew);
+                msnew.Position = 0;
+                return msnew;
             }
         }
 
-        public static void addStream(string filename, Stream s)
+        public static void addStream(string filename, MemoryStream s!!)
         {
             if (null == filename)
                 return;
@@ -224,12 +180,8 @@ public static void addStream(string filename, Stream s)
 
             lock (s_XmlFileMemoryCacheLock)
             {
+                // overwrite any existing
                 s_XmlFileInMemoryCache[NormalizeFilePath(filename)] = s;
-
-                MemoryStream msbak = new MemoryStream();
-                s.Position = 0;
-                s.CopyTo(msbak);
-                s_XmlFileInMemoryCacheBackup[NormalizeFilePath(filename)] = msbak;
             }
         }
 
diff --git a/src/libraries/Common/tests/System/Xml/XmlCoreTest/WriterFactory.cs b/src/libraries/Common/tests/System/Xml/XmlCoreTest/WriterFactory.cs
index da853e3ed720..dfa238e09b43 100644
--- a/src/libraries/Common/tests/System/Xml/XmlCoreTest/WriterFactory.cs
+++ b/src/libraries/Common/tests/System/Xml/XmlCoreTest/WriterFactory.cs
@@ -60,7 +60,7 @@ public WriterFactory(WriterType t, bool overrideAsync = false, bool async = fals
 
         private XmlWriterSettings _wSettings = null;
         private XmlWriter _xmlWriter = null;
-        private Stream _writerStream = null;
+        private MemoryStream _writerStream = null;
 
         XmlWriter CreateWriterImpl()
         {
@@ -90,9 +90,8 @@ XmlWriter CreateWriterImpl()
                     _wSettings.CloseOutput = false;
                     if (_overrideAsync)
                         _wSettings.Async = _async;
-
+                    _xmlWriter = new CustomWriter(_writerStream, _wSettings);
                     FilePathUtil.addStream(_fileName, _writerStream);
-                    _xmlWriter = new CustomWriter(_fileName, _wSettings);
                     break;
                 case WriterType.UTF8WriterIndent:
                     _writerStream = new MemoryStream();
diff --git a/src/libraries/System.Private.Xml/tests/Readers/NameTable/TestFiles.cs b/src/libraries/System.Private.Xml/tests/Readers/NameTable/TestFiles.cs
index 1000023e72f4..701b48032ed3 100644
--- a/src/libraries/System.Private.Xml/tests/Readers/NameTable/TestFiles.cs
+++ b/src/libraries/System.Private.Xml/tests/Readers/NameTable/TestFiles.cs
@@ -79,7 +79,7 @@ protected static void DeleteTestFile(string strFileName)
         public static void CreateGenericTestFile(string strFileName)
         {
             MemoryStream ms = new MemoryStream();
-            TextWriter tw = new StreamWriter(ms);
+            using var tw = new StreamWriter(ms, encoding:null, bufferSize:-1, leaveOpen:true);
 
             tw.WriteLine("<?xml version=\"1.0\" encoding=\"UTF-8\" standalone=\"no\"?>");
             tw.WriteLine("<!-- comment1 -->");
@@ -170,7 +170,6 @@ public static void CreateGenericTestFile(string strFileName)
             tw.WriteLine("<CHARS_COMMENT1>xxx<!-- comment1-->zzz</CHARS_COMMENT1>");
             tw.WriteLine("<CHARS_COMMENT2><!-- comment1-->zzz</CHARS_COMMENT2>");
             tw.WriteLine("<CHARS_COMMENT3>xxx<!-- comment1--></CHARS_COMMENT3>");
-            tw.Flush();
             tw.WriteLine("<ISDEFAULT />");
             tw.WriteLine("<ISDEFAULT a1='a1value' />");
             tw.WriteLine("<BOOLEAN1>true</BOOLEAN1>");
@@ -202,7 +201,6 @@ public static void CreateGenericTestFile(string strFileName)
             tw.WriteLine("<GRPDESCR>twin brothers, and sons to Aegeon and Aemilia.</GRPDESCR>");
             tw.WriteLine("</PGROUP>");
             tw.WriteLine("<PGROUP>");
-            tw.Flush();
             tw.WriteLine("<XMLLANG0 xml:lang=\"en-US\">What color e1foo is it?</XMLLANG0>");
             tw.Write("<XMLLANG1 xml:lang=\"en-GB\">What color is it?<a><b><c>Language Test</c><PERSONA>DROMIO OF EPHESUS</PERSONA></b></a></XMLLANG1>");
             tw.WriteLine("<NOXMLLANG />");
@@ -269,28 +267,26 @@ public static void CreateGenericTestFile(string strFileName)
 
 
             tw.Write("</PLAY>");
-            tw.Flush();
+
             FilePathUtil.addStream(strFileName, ms);
         }
 
         public static void CreateBigElementTestFile(string strFileName)
         {
             MemoryStream ms = new MemoryStream();
-            TextWriter tw = new StreamWriter(ms);
+            using var tw = new StreamWriter(ms, encoding:null, bufferSize:-1, leaveOpen:true);
 
             string str = new string('Z', (1 << 20) - 1);
             tw.WriteLine("<Root>");
             tw.Write("<");
             tw.Write(str);
             tw.WriteLine("X />");
-            tw.Flush();
 
             tw.Write("<");
             tw.Write(str);
             tw.WriteLine("Y />");
             tw.WriteLine("</Root>");
 
-            tw.Flush();
             FilePathUtil.addStream(strFileName, ms);
         }
     }
diff --git a/src/libraries/System.Private.Xml/tests/Writers/XmlWriterApi/TCFullEndElement.cs b/src/libraries/System.Private.Xml/tests/Writers/XmlWriterApi/TCFullEndElement.cs
index 0e2e261ea494..d50456ce3746 100644
--- a/src/libraries/System.Private.Xml/tests/Writers/XmlWriterApi/TCFullEndElement.cs
+++ b/src/libraries/System.Private.Xml/tests/Writers/XmlWriterApi/TCFullEndElement.cs
@@ -6352,12 +6352,12 @@ public partial class TCClose
                 [XmlWriterInlineData]
                 public void var_1(XmlWriterUtils utils)
                 {
-                    using (XmlWriter writer = utils.CreateWriter())
-                    {
-                        writer.WriteStartElement("Root");
-                        writer.WriteStartElement("Nesting");
-                        writer.WriteStartElement("SomeDeep");
-                    }
+                    XmlWriter writer = utils.CreateWriter();
+                    writer.WriteStartElement("Root");
+                    writer.WriteStartElement("Nesting");
+                    writer.WriteStartElement("SomeDeep");
+                    writer.Close();
+
                     Assert.True(utils.CompareReader("<Root><Nesting><SomeDeep /></Nesting></Root>"));
                 }
 
diff --git a/src/libraries/System.Private.Xml/tests/XmlReaderLib/TestFiles.cs b/src/libraries/System.Private.Xml/tests/XmlReaderLib/TestFiles.cs
index 04c08d8247f8..efcc2a2d40d7 100644
--- a/src/libraries/System.Private.Xml/tests/XmlReaderLib/TestFiles.cs
+++ b/src/libraries/System.Private.Xml/tests/XmlReaderLib/TestFiles.cs
@@ -291,42 +291,42 @@ protected static void DeleteTestFile(string strFileName)
 
         public static void CreateByteTestFile(string strFileName)
         {
-            Stream s = new MemoryStream();
-            TextWriter tw = new StreamWriter(s);
+            var s = new MemoryStream();
+            using var tw = new StreamWriter(s, encoding:null, bufferSize:-1, leaveOpen:true);
+
             tw.WriteLine("x");
-            tw.Flush();
+
             FilePathUtil.addStream(strFileName, s);
         }
 
         public static void CreateUTF8EncodedTestFile(string strFileName, Encoding encode)
         {
-            Stream strm = new MemoryStream();
-            TextWriter tw = new StreamWriter(strm, encode);
+            var s = new MemoryStream();
+            using var tw = new StreamWriter(s, encode, bufferSize:-1, leaveOpen:true);
 
             tw.WriteLine("<root>");
             tw.Write("\u00A9");
             tw.WriteLine("</root>");
 
-            tw.Flush();
-            FilePathUtil.addStream(strFileName, strm);
+            FilePathUtil.addStream(strFileName, s);
         }
 
         public static void CreateEncodedTestFile(string strFileName, Encoding encode)
         {
-            Stream strm = new MemoryStream();
-            TextWriter tw = new StreamWriter(strm, encode);
+            var s = new MemoryStream();
+            using var tw = new StreamWriter(s, encode, bufferSize:-1, leaveOpen:true);
 
             tw.WriteLine("<root>");
             tw.WriteLine("</root>");
 
-            tw.Flush();
-            FilePathUtil.addStream(strFileName, strm);
+            FilePathUtil.addStream(strFileName, s);
         }
 
         public static void CreateWhitespaceHandlingTestFile(string strFileName)
         {
-            Stream s = new MemoryStream();
-            TextWriter tw = new StreamWriter(s);
+            var s = new MemoryStream();
+            using var tw = new StreamWriter(s, encoding:null, bufferSize:-1, leaveOpen:true);
+
             tw.WriteLine("<!DOCTYPE dt [");
             tw.WriteLine("<!ELEMENT WHITESPACE1 (#PCDATA)*>");
             tw.WriteLine("<!ELEMENT WHITESPACE2 (#PCDATA)*>");
@@ -337,7 +337,7 @@ public static void CreateWhitespaceHandlingTestFile(string strFileName)
             tw.WriteLine("<WHITESPACE2> <ELEM /> </WHITESPACE2>");
             tw.WriteLine("<WHITESPACE3>\t<ELEM />\t</WHITESPACE3>");
             tw.WriteLine("</doc>");
-            tw.Flush();
+
             FilePathUtil.addStream(strFileName, s);
         }
 
@@ -350,8 +350,9 @@ public static void CreateGenericXsltTestFile(string strFileName)
         }
         public static void CreateGenericTestFile(string strFileName)
         {
-            Stream s = new MemoryStream();
-            TextWriter tw = new StreamWriter(s);
+            var s = new MemoryStream();
+            using var tw = new StreamWriter(s, encoding:null, bufferSize:-1, leaveOpen:true);
+
             tw.WriteLine("<?xml version=\"1.0\" encoding=\"UTF-8\" standalone=\"no\"?>");
             tw.WriteLine("<!-- comment1 -->");
             tw.WriteLine("<?PI1_First processing instruction?>");
@@ -425,7 +426,6 @@ public static void CreateGenericTestFile(string strFileName)
             tw.WriteLine("<CHARS_COMMENT1>xxx<!-- comment1-->zzz</CHARS_COMMENT1>");
             tw.WriteLine("<CHARS_COMMENT2><!-- comment1-->zzz</CHARS_COMMENT2>");
             tw.WriteLine("<CHARS_COMMENT3>xxx<!-- comment1--></CHARS_COMMENT3>");
-            tw.Flush();
             tw.WriteLine("<ISDEFAULT />");
             tw.WriteLine("<ISDEFAULT a1='a1value' />");
             tw.WriteLine("<BOOLEAN1>true</BOOLEAN1>");
@@ -457,7 +457,6 @@ public static void CreateGenericTestFile(string strFileName)
             tw.WriteLine("<GRPDESCR>twin brothers, and sons to Aegeon and Aemilia.</GRPDESCR>");
             tw.WriteLine("</PGROUP>");
             tw.WriteLine("<PGROUP>");
-            tw.Flush();
             tw.WriteLine("<XMLLANG0 xml:lang=\"en-US\">What color NO_REFERENCEe1; is it?</XMLLANG0>");
             tw.Write("<XMLLANG1 xml:lang=\"en-GB\">What color is it?<a><b><c>Language Test</c><PERSONA>DROMIO OF EPHESUS</PERSONA></b></a></XMLLANG1>");
             tw.WriteLine("<NOXMLLANG />");
@@ -523,7 +522,6 @@ public static void CreateGenericTestFile(string strFileName)
             tw.WriteLine("<VALIDXMLLANG3 xml:lang=\"a b-cd\" />");
 
             tw.Write("</PLAY>");
-            tw.Flush();
             FilePathUtil.addStream(strFileName, s);
         }
 
@@ -561,17 +559,18 @@ public static void CreateXDRTestFile(string strFileName)
 
         public static void CreateInvalidNamespaceTestFile(string strFileName)
         {
-            Stream s = new MemoryStream();
-            TextWriter tw = new StreamWriter(s);
+            var s = new MemoryStream();
+            using var tw = new StreamWriter(s, encoding:null, bufferSize:-1, leaveOpen:true);
+
             tw.WriteLine("<NAMESPACE0 xmlns:bar=\"1\"><bar1:check>Namespace=1</bar1:check></NAMESPACE0>");
-            tw.Flush();
+
             FilePathUtil.addStream(strFileName, s);
         }
 
         public static void CreateNamespaceTestFile(string strFileName)
         {
-            Stream s = new MemoryStream();
-            TextWriter tw = new StreamWriter(s);
+            var s = new MemoryStream();
+            using var tw = new StreamWriter(s, encoding:null, bufferSize:-1, leaveOpen:true);
 
             tw.WriteLine("<DOCNAMESPACE>");
             tw.WriteLine("<NAMESPACE0 xmlns:bar=\"1\"><bar:check>Namespace=1</bar:check></NAMESPACE0>");
@@ -585,14 +584,15 @@ public static void CreateNamespaceTestFile(string strFileName)
             tw.WriteLine("<a13 a:check=\"Namespace=13\" xmlns:a=\"13\" /><check14 xmlns=\"14\">Namespace=14</check14></NAMESPACE3>");
             tw.WriteLine("<NONAMESPACE>Namespace=\"\"</NONAMESPACE>");
             tw.WriteLine("</DOCNAMESPACE>");
-            tw.Flush();
+
             FilePathUtil.addStream(strFileName, s);
         }
 
         public static void CreateXmlLangTestFile(string strFileName)
         {
-            Stream s = new MemoryStream();
-            TextWriter tw = new StreamWriter(s);
+            var s = new MemoryStream();
+            using var tw = new StreamWriter(s, encoding:null, bufferSize:-1, leaveOpen:true);
+
             tw.WriteLine("<PGROUP>");
             tw.WriteLine("<PERSONA>DROMIO OF EPHESUS</PERSONA>");
             tw.WriteLine("<PERSONA>DROMIO OF SYRACUSE</PERSONA>");
@@ -603,14 +603,14 @@ public static void CreateXmlLangTestFile(string strFileName)
             tw.WriteLine("<XMLLANG2 xml:lang=\"en-US\">What color is it?<TITLE><!-- this is a comment--></TITLE><XMLLANG1 xml:lang=\"en-GB\">Testing language<XMLLANG0 xml:lang=\"en-US\">What color is it?</XMLLANG0>haha </XMLLANG1>hihihi</XMLLANG2>");
             tw.WriteLine("<DONEXMLLANG />");
             tw.WriteLine("</PGROUP>");
-            tw.Flush();
+
             FilePathUtil.addStream(strFileName, s);
         }
 
         public static void CreateXmlSpaceTestFile(string strFileName)
         {
-            Stream s = new MemoryStream();
-            TextWriter tw = new StreamWriter(s);
+            var s = new MemoryStream();
+            using var tw = new StreamWriter(s, encoding:null, bufferSize:-1, leaveOpen:true);
 
             tw.WriteLine("<PGROUP>");
             tw.WriteLine("<PERSONA>DROMIO OF EPHESUS</PERSONA>");
@@ -622,18 +622,18 @@ public static void CreateXmlSpaceTestFile(string strFileName)
             tw.WriteLine("<XMLSPACE2A xml:space=\'default\'>&lt; <XMLSPACE3 xml:space=\'preserve\'>  &lt; &gt; <XMLSPACE4 xml:space=\'default\'>  &lt; &gt;  </XMLSPACE4> test </XMLSPACE3> &gt;</XMLSPACE2A>");
             tw.WriteLine("<GRPDESCR>twin brothers, and attendants on the two Antipholuses.</GRPDESCR>");
             tw.WriteLine("</PGROUP>");
-            tw.Flush();
+
             FilePathUtil.addStream(strFileName, s);
         }
 
         public static void CreateJunkTestFile(string strFileName)
         {
-            Stream s = new MemoryStream();
-            TextWriter tw = new StreamWriter(s);
+            var s = new MemoryStream();
+            using var tw = new StreamWriter(s, encoding:null, bufferSize:-1, leaveOpen:true);
 
             string str = new string('Z', (1 << 20) - 1);
             tw.Write(str);
-            tw.Flush();
+
             FilePathUtil.addStream(strFileName, s);
         }
 
@@ -661,8 +661,10 @@ public static void CreateBase64TestFile(string strFileName)
             {
                 WriteToBuffer(ref WTextOnly, ref WTextOnlylen, System.BitConverter.GetBytes(strBase64[i]));
             }
-            MemoryStream mems = new MemoryStream();
-            XmlWriter w = XmlWriter.Create(mems, null);
+
+            var mems = new MemoryStream();
+            using var w = XmlWriter.Create(mems, new XmlWriterSettings { CloseOutput = false });
+
             w.WriteStartDocument();
             w.WriteStartElement("Root");
             w.WriteStartElement("ElemAll");
@@ -697,7 +699,7 @@ public static void CreateBase64TestFile(string strFileName)
             w.WriteRaw("D2BAa<MIX></MIX>AQID");
             w.WriteEndElement();
             w.WriteEndElement();
-            w.Flush();
+
             FilePathUtil.addStream(strFileName, mems);
         }
 
@@ -725,14 +727,14 @@ public static void CreateBinHexTestFile(string strFileName)
             {
                 WriteToBuffer(ref WTextOnly, ref WTextOnlylen, System.BitConverter.GetBytes(strBinHex[i]));
             }
-            MemoryStream mems = new MemoryStream();
 
-            XmlWriter w = XmlWriter.Create(mems);
+            var mems = new MemoryStream();
+            using var w = XmlWriter.Create(mems, new XmlWriterSettings { CloseOutput = false });
+
             w.WriteStartElement("Root");
             w.WriteStartElement("ElemAll");
             w.WriteBinHex(Wbinhex, 0, (int)Wbinhexlen);
             w.WriteEndElement();
-            w.Flush();
 
             w.WriteStartElement("ElemEmpty");
             w.WriteString(string.Empty);
@@ -759,68 +761,67 @@ public static void CreateBinHexTestFile(string strFileName)
             w.WriteElementString("ElemErr", "a&A2A3");
 
             w.WriteEndElement();
-            w.Flush();
+
             FilePathUtil.addStream(strFileName, mems);
         }
 
         public static void CreateBigElementTestFile(string strFileName)
         {
-            Stream s = new MemoryStream();
-            TextWriter tw = new StreamWriter(s);
+            var s = new MemoryStream();
+            using var tw = new StreamWriter(s, encoding:null, bufferSize:-1, leaveOpen:true);
 
             string str = new string('Z', (1 << 20) - 1);
             tw.WriteLine("<Root>");
             tw.Write("<");
             tw.Write(str);
             tw.WriteLine("X />");
-            tw.Flush();
 
             tw.Write("<");
             tw.Write(str);
             tw.WriteLine("Y />");
             tw.WriteLine("</Root>");
 
-            tw.Flush();
             FilePathUtil.addStream(strFileName, s);
         }
         public static void CreateXSLTStyleSheetWCopyTestFile(string strFileName)
         {
-            Stream s = new MemoryStream();
-            TextWriter tw = new StreamWriter(s);
+            var s = new MemoryStream();
+            using var tw = new StreamWriter(s, encoding:null, bufferSize:-1, leaveOpen:true);
+
             tw.WriteLine("<xsl:stylesheet version=\"1.0\" xmlns:xsl=\"http://www.w3.org/1999/XSL/Transform\">");
             tw.WriteLine("<xsl:template match=\"/\">");
             tw.WriteLine("<xsl:copy-of select=\"/\" />");
             tw.WriteLine("</xsl:template>");
             tw.WriteLine("</xsl:stylesheet>");
-            tw.Flush();
+
             FilePathUtil.addStream(strFileName, s);
         }
 
         public static void CreateConstructorTestFile(string strFileName)
         {
-            Stream s = new MemoryStream();
-            TextWriter tw = new StreamWriter(s);
+            var s = new MemoryStream();
+            using var tw = new StreamWriter(s, encoding:null, bufferSize:-1, leaveOpen:true);
 
             tw.WriteLine("<?xml version=\"1.0\"?>");
             tw.WriteLine("<ROOT>");
             tw.WriteLine("<ATTRIBUTE3 a1='a1value' a2='a2value' a3='a3value' />");
             tw.Write("</ROOT>");
-            tw.Flush();
+
             FilePathUtil.addStream(strFileName, s);
         }
 
         public static void CreateLineNumberTestFile(string strFileName)
         {
-            Stream s = new MemoryStream();
-            TextWriter tw = new StreamWriter(s);
+            var s = new MemoryStream();
+            using var tw = new StreamWriter(s, encoding:null, bufferSize:-1, leaveOpen:true);
 
             FilePathUtil.addStream(strFileName, s);
         }
 
         public static void CreateLbNormalizationTestFile(string strFileName)
         {
-            Stream s = new MemoryStream();
-            TextWriter tw = new StreamWriter(s);
+            var s = new MemoryStream();
+            using var tw = new StreamWriter(s, encoding:null, bufferSize:-1, leaveOpen:true);
 
             FilePathUtil.addStream(strFileName, s);
         }