diff --git a/src/libraries/Common/tests/System/Xml/XmlCoreTest/FilePathUtil.cs b/src/libraries/Common/tests/System/Xml/XmlCoreTest/FilePathUtil.cs
index b5a64db4aab04c..6f5e326ae01a5a 100644
--- a/src/libraries/Common/tests/System/Xml/XmlCoreTest/FilePathUtil.cs
+++ b/src/libraries/Common/tests/System/Xml/XmlCoreTest/FilePathUtil.cs
@@ -120,13 +120,15 @@ static void initXmlFileCacheIfNotYet()
             {
                 if (s_XmlFileInMemoryCache == null)
                 {
-                    s_XmlFileInMemoryCache = new MyDict<string, MemoryStream>();
+                    MyDict<string, MemoryStream> cache = new MyDict<string, MemoryStream>();
 
                     foreach (Tuple<string, byte[]> file in GetDataFiles())
                     {
                         var ms = new MemoryStream(file.Item2);
-                        s_XmlFileInMemoryCache[NormalizeFilePath(file.Item1)] = ms;
+                        cache[NormalizeFilePath(file.Item1)] = ms;
                     }
+
+                    s_XmlFileInMemoryCache = cache;
                 }
             }
         }
diff --git a/src/libraries/System.Private.Xml.Linq/tests/XDocument.Common/BridgeHelpers.cs b/src/libraries/System.Private.Xml.Linq/tests/XDocument.Common/BridgeHelpers.cs
index d8fd205bd2a22d..7e24986509a9a0 100644
--- a/src/libraries/System.Private.Xml.Linq/tests/XDocument.Common/BridgeHelpers.cs
+++ b/src/libraries/System.Private.Xml.Linq/tests/XDocument.Common/BridgeHelpers.cs
@@ -539,42 +539,42 @@ public static void DeleteTestFile(string strFileName)
 
         public static void CreateByteTestFile(string strFileName)
         {
-            FilePathUtil.addStream(strFileName, new MemoryStream());
-            TextWriter tw = new StreamWriter(FilePathUtil.getStream(strFileName));
+            var ms = new MemoryStream();
+            using var tw = new StreamWriter(ms, leaveOpen: true);
             tw.WriteLine("x");
-            tw.Flush();
-            tw.Dispose();
+
+            FilePathUtil.addStream(strFileName, ms);
         }
 
         public static void CreateUTF8EncodedTestFile(string strFileName, Encoding encode)
         {
-            FilePathUtil.addStream(strFileName, new MemoryStream());
-            TextWriter tw = new StreamWriter(FilePathUtil.getStream(strFileName), encode);
+            var ms = new MemoryStream();
+            using var tw = new StreamWriter(ms, encoding: encode, leaveOpen: true);
 
             tw.WriteLine("<root>");
             tw.Write("\uFFFD");
             tw.WriteLine("</root>");
 
-            tw.Flush();
-            tw.Dispose();
+            FilePathUtil.addStream(strFileName, ms);
         }
 
         public static void CreateEncodedTestFile(string strFileName, Encoding encode)
         {
-            FilePathUtil.addStream(strFileName, new MemoryStream());
-            TextWriter tw = new StreamWriter(FilePathUtil.getStream(strFileName), encode);
+            var ms = new MemoryStream();
+            
+            using var tw = new StreamWriter(ms, encoding: encode, leaveOpen: true);
 
             tw.WriteLine("<root>");
             tw.WriteLine("</root>");
 
-            tw.Flush();
-            tw.Dispose();
+            FilePathUtil.addStream(strFileName, ms);
         }
 
         public static void CreateWhitespaceHandlingTestFile(string strFileName)
         {
-            FilePathUtil.addStream(strFileName, new MemoryStream());
-            TextWriter tw = new StreamWriter(FilePathUtil.getStream(strFileName));
+            var ms = new MemoryStream();
+            
+            using var tw = new StreamWriter(ms, leaveOpen: true);
 
             tw.WriteLine("<!DOCTYPE dt [");
             tw.WriteLine("<!ELEMENT WHITESPACE1 (#PCDATA)*>");
@@ -586,8 +586,8 @@ public static void CreateWhitespaceHandlingTestFile(string strFileName)
             tw.WriteLine("<WHITESPACE2> <ELEM /> </WHITESPACE2>");
             tw.WriteLine("<WHITESPACE3>\t<ELEM />\t</WHITESPACE3>");
             tw.WriteLine("</doc>");
-            tw.Flush();
-            tw.Dispose();
+
+            FilePathUtil.addStream(strFileName, ms);
         }
 
         public static void CreateGenericXsltTestFile(string strFileName)
@@ -598,8 +598,9 @@ public static void CreateGenericXsltTestFile(string strFileName)
 
         public static void CreateGenericTestFile(string strFileName)
         {
-            FilePathUtil.addStream(strFileName, new MemoryStream());
-            TextWriter tw = new StreamWriter(FilePathUtil.getStream(strFileName));
+            var ms = new MemoryStream();
+            
+            using var tw = new StreamWriter(ms, leaveOpen: true);
 
             tw.WriteLine("<?xml version=\"1.0\" encoding=\"UTF-8\" standalone=\"no\"?>");
             tw.WriteLine("<!-- comment1 -->");
@@ -791,11 +792,12 @@ public static void CreateGenericTestFile(string strFileName)
             tw.WriteLine("<VALIDXMLLANG3 xml:lang=\"a b-cd\" />");
 
             tw.Write("</PLAY>");
-            tw.Flush();
+
+            FilePathUtil.addStream(strFileName, ms);
 
             //Create external DTD file
-            FilePathUtil.addStream("AllNodeTypes.dtd", new MemoryStream());
-            TextWriter twDTD = new StreamWriter(FilePathUtil.getStream("AllNodeTypes.dtd"));
+            var msDTD = new MemoryStream();
+            using var twDTD = new StreamWriter(msDTD, leaveOpen: true);
             twDTD.WriteLine("<!ELEMENT elem2 (#PCDATA| a | b )* >");
             twDTD.WriteLine("<!ELEMENT a ANY>");
             twDTD.WriteLine("<!ELEMENT b ANY>");
@@ -805,68 +807,75 @@ public static void CreateGenericTestFile(string strFileName)
             twDTD.WriteLine("att2 CDATA #IMPLIED");
             twDTD.WriteLine("att3 CDATA #IMPLIED>");
             twDTD.WriteLine("<!ATTLIST a refs IDREFS #IMPLIED>");
-            twDTD.Flush();
+            
+            FilePathUtil.addStream("AllNodeTypes.dtd", msDTD);
 
             // Create Ent file
-            FilePathUtil.addStream("AllNodeTypes.ent", new MemoryStream());
-            TextWriter twENT = new StreamWriter(FilePathUtil.getStream("AllNodeTypes.ent"));
+            var msENT = new MemoryStream();
+            using var twENT = new StreamWriter(msENT, leaveOpen: true);
             twENT.WriteLine("<!ELEMENT foo ANY>");
             twENT.WriteLine("<!ENTITY % ext4 \"blah\">");
             twENT.WriteLine("<!ENTITY ext3 \"%ext4;\">");
-            twENT.Flush();
+
+            FilePathUtil.addStream("AllNodeTypes.ent", msENT);
         }
 
         public static void CreateInvalidDTDTestFile(string strFileName)
         {
-            TextWriter tw = new StreamWriter(FilePathUtil.getStream(strFileName));
+            var ms = new MemoryStream();
+            using var tw = new StreamWriter(ms, leaveOpen: true);
 
             tw.WriteLine("<?xml version=\"1.0\"?><!DOCTYPE Root [<!ELEMENT Root ANY><!ELEMENT E ANY><!ATTLIST E	A1 NOTATION (N) #IMPLIED>]>");
             tw.WriteLine("<Root><E A1=\"N\" /></Root>");
-            tw.Flush();
-            tw.Dispose();
+
+            FilePathUtil.addStream(strFileName, ms);
         }
 
         public static void CreateValidDTDTestFile(string strFileName)
         {
-            TextWriter tw = new StreamWriter(FilePathUtil.getStream(strFileName));
+            var ms = new MemoryStream();
+            using var tw = new StreamWriter(ms, leaveOpen: true);
 
             tw.WriteLine("<?xml version=\"1.0\"?><!DOCTYPE Root [<!ELEMENT Root ANY><!ELEMENT E ANY><!ATTLIST E	IMAGE_FORMAT (bmp|jpg|gif) #IMPLIED>]>");
             tw.Write("<Root><E A1=\"gif\" /></Root>");
-            tw.Flush();
-            tw.Dispose();
+
+            FilePathUtil.addStream(strFileName, ms);
         }
 
         public static void CreateWellFormedDTDTestFile(string strFileName)
         {
-            TextWriter tw = new StreamWriter(FilePathUtil.getStream(strFileName));
+            var ms = new MemoryStream();
+            using var tw = new StreamWriter(ms, leaveOpen: true);
 
             tw.Write("<!DOCTYPE foo [<!ELEMENT foo (e1, e2, e3)><!ENTITY bar \"<e1> <e4 /> </e1> <e2> that </e2>\">");
             tw.Write("<!ELEMENT e1 (e4)><!ELEMENT e2 ANY><!ELEMENT e3 ANY><!ELEMENT e4 ANY>]>");
             tw.Write("<foo>&bar;<e3 /></foo>");
-            tw.Flush();
-            tw.Dispose();
+
+            FilePathUtil.addStream(strFileName, ms);
         }
 
         public static void CreateNonWellFormedDTDTestFile(string strFileName)
         {
-            TextWriter tw = new StreamWriter(FilePathUtil.getStream(strFileName));
+            var ms = new MemoryStream();
+            using var tw = new StreamWriter(ms, leaveOpen: true);
 
             tw.Write("<!DOCTYPE foo [<!ELEMENT foo (e1, e2, e3)><!ENTITY bar \"<e1> <e4 /> </e1> <e2> that </e2></e2>\">");
             tw.Write("<!ELEMENT e1 (e4)><!ELEMENT e2 ANY><!ELEMENT e3 ANY><!ELEMENT e4 ANY>]>");
             tw.Write("<foo>&bar;<e3 /></foo>");
-            tw.Flush();
-            tw.Dispose();
+
+            FilePathUtil.addStream(strFileName, ms);
         }
 
         public static void CreateInvWellFormedDTDTestFile(string strFileName)
         {
-            TextWriter tw = new StreamWriter(FilePathUtil.getStream(strFileName));
+            var ms = new MemoryStream();
+            using var tw = new StreamWriter(ms, leaveOpen: true);
 
             tw.Write("<!DOCTYPE foo [<!ELEMENT foo (e1, e2, e3)><!ENTITY bar \"<e1> this </e1> <e2> that </e2>\">");
             tw.Write("<!ELEMENT e1 (e4)><!ELEMENT e2 ANY><!ELEMENT e3 ANY><!ELEMENT e4 ANY>]>");
             tw.Write("<foo>&bar;<e3 /></foo>");
-            tw.Flush();
-            tw.Dispose();
+
+            FilePathUtil.addStream(strFileName, ms);
         }
 
         public static void CreateInvalidXMLXDRTestFile(string strFileName)
@@ -874,12 +883,13 @@ public static void CreateInvalidXMLXDRTestFile(string strFileName)
             // Create XDR before
             CreateXDRTestFile(pValidXDR);
 
-            TextWriter tw = new StreamWriter(FilePathUtil.getStream(strFileName));
+            var ms = new MemoryStream();
+            using var tw = new StreamWriter(ms, leaveOpen: true);
 
             tw.WriteLine("<?xml version=\"1.0\" ?><e:Root xmlns:e=\"x-schema:xdrfile.xml\">");
             tw.WriteLine("<e:e1>Element 1</e:e1></e:Root>");
-            tw.Flush();
-            tw.Dispose();
+
+            FilePathUtil.addStream(strFileName, ms);
         }
 
         public static void CreateXDRXMLTestFile(string strFileName)
@@ -887,36 +897,40 @@ public static void CreateXDRXMLTestFile(string strFileName)
             // Create XDR before
             CreateXDRTestFile(pValidXDR);
 
-            TextWriter tw = new StreamWriter(FilePathUtil.getStream(strFileName));
+            var ms = new MemoryStream();
+            using var tw = new StreamWriter(ms, leaveOpen: true);
 
             tw.WriteLine("<bar xmlns=\"x-schema:XdrFile.xml\"> <tt /> <tt /></bar>");
-            tw.Flush();
-            tw.Dispose();
+
+            FilePathUtil.addStream(strFileName, ms);
         }
 
         public static void CreateXDRTestFile(string strFileName)
         {
-            TextWriter tw = new StreamWriter(FilePathUtil.getStream(strFileName));
+            var ms = new MemoryStream();
+            using var tw = new StreamWriter(ms, leaveOpen: true);
 
             tw.WriteLine("<Schema xmlns=\"uuid:BDC6E3F0-6DA3-11d1-A2A3-00AA00C14882\"><ElementType content=\"empty\" name=\"tt\"></ElementType>");
             tw.WriteLine("<ElementType content=\"eltOnly\" order=\"seq\" name=\"bar\" model=\"closed\"><element type=\"tt\" /><element type=\"tt\" /></ElementType>");
             tw.WriteLine("</Schema>");
-            tw.Flush();
-            tw.Dispose();
+
+            FilePathUtil.addStream(strFileName, ms);
         }
 
         public static void CreateInvalidNamespaceTestFile(string strFileName)
         {
-            TextWriter tw = new StreamWriter(FilePathUtil.getStream(strFileName));
+            var ms = new MemoryStream();
+            using var tw = new StreamWriter(ms, leaveOpen: true);
 
             tw.WriteLine("<NAMESPACE0 xmlns:bar=\"1\"><bar1:check>Namespace=1</bar1:check></NAMESPACE0>");
-            tw.Flush();
-            tw.Dispose();
+
+            FilePathUtil.addStream(strFileName, ms);
         }
 
         public static void CreateNamespaceTestFile(string strFileName)
         {
-            TextWriter tw = new StreamWriter(FilePathUtil.getStream(strFileName));
+            var ms = new MemoryStream();
+            using var tw = new StreamWriter(ms, leaveOpen: true);
 
             tw.WriteLine("<DOCNAMESPACE>");
             tw.WriteLine("<NAMESPACE0 xmlns:bar=\"1\"><bar:check>Namespace=1</bar:check></NAMESPACE0>");
@@ -930,13 +944,14 @@ 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();
-            tw.Dispose();
+
+            FilePathUtil.addStream(strFileName, ms);
         }
 
         public static void CreateXmlLangTestFile(string strFileName)
         {
-            TextWriter tw = new StreamWriter(FilePathUtil.getStream(strFileName));
+            var ms = new MemoryStream();
+            using var tw = new StreamWriter(ms, leaveOpen: true);
 
             tw.WriteLine("<PGROUP>");
             tw.WriteLine("<PERSONA>DROMIO OF EPHESUS</PERSONA>");
@@ -948,13 +963,14 @@ 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();
-            tw.Dispose();
+
+            FilePathUtil.addStream(strFileName, ms);
         }
 
         public static void CreateXmlSpaceTestFile(string strFileName)
         {
-            TextWriter tw = new StreamWriter(FilePathUtil.getStream(strFileName));
+            var ms = new MemoryStream();
+            using var tw = new StreamWriter(ms, leaveOpen: true);
 
             tw.WriteLine("<PGROUP>");
             tw.WriteLine("<PERSONA>DROMIO OF EPHESUS</PERSONA>");
@@ -966,18 +982,19 @@ 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();
-            tw.Dispose();
+
+            FilePathUtil.addStream(strFileName, ms);
         }
 
         public static void CreateJunkTestFile(string strFileName)
         {
-            TextWriter tw = new StreamWriter(FilePathUtil.getStream(strFileName));
+            var ms = new MemoryStream();
+            using var tw = new StreamWriter(ms, leaveOpen: true);
 
             string str = new string('Z', (1 << 20) - 1);
             tw.Write(str);
-            tw.Flush();
-            tw.Dispose();
+
+            FilePathUtil.addStream(strFileName, ms);
         }
 
         public static void CreateBase64TestFile(string strFileName)
@@ -1005,9 +1022,8 @@ public static void CreateBase64TestFile(string strFileName)
                 WriteToBuffer(ref WTextOnly, ref WTextOnlylen, System.BitConverter.GetBytes(strBase64[i]));
             }
 
-            FilePathUtil.addStream(strFileName, new MemoryStream());
-
-            XmlWriter w = XmlWriter.Create(FilePathUtil.getStream(strFileName));
+            var ms = new MemoryStream();
+            using var w = XmlWriter.Create(ms);
             w.WriteStartDocument();
             w.WriteDocType("Root", null, null, "<!ENTITY e 'abc'>");
             w.WriteStartElement("Root");
@@ -1043,7 +1059,8 @@ public static void CreateBase64TestFile(string strFileName)
             w.WriteRaw("D2BAa<MIX>abc</MIX>AQID");
             w.WriteEndElement();
             w.WriteEndElement();
-            w.Flush();
+
+            FilePathUtil.addStream(strFileName, ms);
         }
 
         public static void CreateBinHexTestFile(string strFileName)
@@ -1070,9 +1087,10 @@ public static void CreateBinHexTestFile(string strFileName)
             {
                 WriteToBuffer(ref WTextOnly, ref WTextOnlylen, System.BitConverter.GetBytes(strBinHex[i]));
             }
-            FilePathUtil.addStream(strFileName, new MemoryStream());
 
-            XmlWriter w = XmlWriter.Create(FilePathUtil.getStream(strFileName));
+            var ms = new MemoryStream();
+
+            using var w = XmlWriter.Create(ms);
             w.WriteStartElement("Root");
             w.WriteStartElement("ElemAll");
             w.WriteBinHex(Wbinhex, 0, (int)Wbinhexlen);
@@ -1104,13 +1122,14 @@ public static void CreateBinHexTestFile(string strFileName)
             w.WriteElementString("ElemErr", "a&A2A3");
 
             w.WriteEndElement();
-            w.Flush();
-            w.Dispose();
+
+            FilePathUtil.addStream(strFileName, ms);
         }
 
         public static void CreateBigElementTestFile(string strFileName)
         {
-            TextWriter tw = new StreamWriter(FilePathUtil.getStream(strFileName));
+            var ms = new MemoryStream();
+            using var tw = new StreamWriter(ms, leaveOpen: true);
 
             string str = new string('Z', (1 << 20) - 1);
             tw.WriteLine("<Root>");
@@ -1124,36 +1143,38 @@ public static void CreateBigElementTestFile(string strFileName)
             tw.WriteLine("Y />");
             tw.WriteLine("</Root>");
 
-            tw.Flush();
-            tw.Dispose();
+            FilePathUtil.addStream(strFileName, ms);
         }
         public static void CreateXSLTStyleSheetWCopyTestFile(string strFileName)
         {
-            TextWriter tw = new StreamWriter(FilePathUtil.getStream(strFileName));
+            var ms = new MemoryStream();
+            using var tw = new StreamWriter(ms, 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();
-            tw.Dispose();
+
+            FilePathUtil.addStream(strFileName, ms);
         }
 
         public static void CreateConstructorTestFile(string strFileName)
         {
-            TextWriter tw = new StreamWriter(FilePathUtil.getStream(strFileName));
+            var ms = new MemoryStream();
+            using var tw = new StreamWriter(ms, 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();
-            tw.Dispose();
+
+            FilePathUtil.addStream(strFileName, ms);
         }
 
         public static void CreateLineNumberTestFile(string strFileName)
         {
-            TextWriter tw = new StreamWriter(FilePathUtil.getStream(strFileName));
+            var ms = new MemoryStream();
+            using var tw = new StreamWriter(ms, leaveOpen: true);
 
             tw.WriteLine("<?xml version=\"1.0\" ?>");
             tw.WriteLine(" <!DOCTYPE DT [");
@@ -1181,22 +1202,23 @@ public static void CreateLineNumberTestFile(string strFileName)
             tw.WriteLine(" <?PI2 abc?>");
             tw.WriteLine("<SIG_WHITESPACE xml:space='preserve'>  </SIG_WHITESPACE>");
             tw.Write("</ROOT>");
-            tw.Flush();
-            tw.Dispose();
+
+            FilePathUtil.addStream(strFileName, ms);
 
             // Create Ent file
-            FilePathUtil.addStream("LineNumber.ent", new MemoryStream());
-            TextWriter twENT = new StreamWriter(FilePathUtil.getStream("LineNumber.ent"));
+            var msENT = new MemoryStream();
+            using var twENT = new StreamWriter(msENT, leaveOpen: true);
             twENT.WriteLine("<!ENTITY % ext4 \"blah\">");
             twENT.WriteLine("<!ENTITY ext31 \"%ext4;\">");
             twENT.WriteLine("<!ENTITY ext3 'zzz'>");
-            twENT.Flush();
-            twENT.Dispose();
+
+            FilePathUtil.addStream("LineNumber.ent", msENT);
         }
 
         public static void CreateLbNormalizationTestFile(string strFileName)
         {
-            TextWriter tw = new StreamWriter(FilePathUtil.getStream(strFileName));
+            var ms = new MemoryStream();
+            using var tw = new StreamWriter(ms, leaveOpen: true);
 
             tw.WriteLine("<?xml version=\"1.0\" standalone=\"no\"?>");
             tw.WriteLine("<!DOCTYPE ROOT");
@@ -1206,28 +1228,35 @@ public static void CreateLbNormalizationTestFile(string strFileName)
             tw.WriteLine("%pe;");
             tw.WriteLine("]>");
             tw.WriteLine("<ROOT>&ge1;&ext1;</ROOT>");
-            tw.Flush();
-            tw.Dispose();
+
+            FilePathUtil.addStream(strFileName, ms);
 
             // Create Ent file
-            FilePathUtil.addStream(pLbNormEnt1, new MemoryStream());
-            TextWriter twENT = new StreamWriter(FilePathUtil.getStream(pLbNormEnt1));
-            twENT.WriteLine("<?xml version=\"1.0\"?>");
-            twENT.WriteLine("<E1 xml:space=\"preserve\">");
-            twENT.WriteLine("</E1>");
-            twENT.WriteLine();
-            twENT.Flush();
-            twENT.Dispose();
+            var msPLbNormEnt1 = new MemoryStream();
+
+            {
+                using var twENT = new StreamWriter(msPLbNormEnt1, leaveOpen: true);
+                twENT.WriteLine("<?xml version=\"1.0\"?>");
+                twENT.WriteLine("<E1 xml:space=\"preserve\">");
+                twENT.WriteLine("</E1>");
+                twENT.WriteLine();
+            }
+
+            FilePathUtil.addStream(pLbNormEnt1, msPLbNormEnt1);
 
             // Create Ent file
-            FilePathUtil.addStream(pLbNormEnt2, new MemoryStream());
-            twENT = new StreamWriter(FilePathUtil.getStream(pLbNormEnt2));
-            twENT.WriteLine("<!ENTITY ext1 \"<E3>");
-            twENT.WriteLine("</E3>\">");
-            twENT.WriteLine("");
-            twENT.WriteLine();
-            twENT.Flush();
-            twENT.Dispose();
+
+            var msPLbNormEnt2 = new MemoryStream();
+
+            {
+                using var twENT = new StreamWriter(msPLbNormEnt2, leaveOpen: true);
+                twENT.WriteLine("<!ENTITY ext1 \"<E3>");
+                twENT.WriteLine("</E3>\">");
+                twENT.WriteLine("");
+                twENT.WriteLine();
+            }
+
+            FilePathUtil.addStream(pLbNormEnt2, msPLbNormEnt2);
         }
 
         public bool FindNodeType(XmlReader r, XmlNodeType _nodetype)
diff --git a/src/libraries/System.Private.Xml.Linq/tests/xNodeReader/ReadBase64.cs b/src/libraries/System.Private.Xml.Linq/tests/xNodeReader/ReadBase64.cs
index 1bc4bee9b2e2a9..29803dff598581 100644
--- a/src/libraries/System.Private.Xml.Linq/tests/xNodeReader/ReadBase64.cs
+++ b/src/libraries/System.Private.Xml.Linq/tests/xNodeReader/ReadBase64.cs
@@ -482,12 +482,15 @@ public void RunBase64DoesnNotRunIntoOverflow()
                     string base64str = Convert.ToBase64String(bits);
 
                     string fileName = "bug105376_" + Variation.Params[0].ToString() + ".xml";
-                    FilePathUtil.addStream(fileName, new MemoryStream());
-                    StreamWriter sw = new StreamWriter(FilePathUtil.getStream(fileName));
-                    sw.Write("<root><base64>");
-                    sw.Write(base64str);
-                    sw.Write("</base64></root>");
-                    sw.Flush();
+                    var ms = new MemoryStream();
+                    {
+                        using var sw = new StreamWriter(ms, leaveOpen: true);
+                        sw.Write("<root><base64>");
+                        sw.Write(base64str);
+                        sw.Write("</base64></root>");
+                    }
+
+                    FilePathUtil.addStream(fileName, ms);
 
                     XmlReader DataReader = GetReader(fileName);
 
@@ -943,14 +946,17 @@ public void ReadBase64DoesNotRunIntoOverflow2()
                     string base64str = Convert.ToBase64String(bits);
 
                     string fileName = "bug105376_" + Variation.Params[0].ToString() + ".xml";
-                    FilePathUtil.addStream(fileName, new MemoryStream());
-                    StreamWriter sw = new StreamWriter(FilePathUtil.getStream(fileName));
-                    sw.Write("<root><base64>");
-                    sw.Write(base64str);
-                    sw.Write("</base64></root>");
-                    sw.Flush();
+                    var ms = new MemoryStream();
+                    {
+                        using var sw = new StreamWriter(ms, leaveOpen: true);
+                        sw.Write("<root><base64>");
+                        sw.Write(base64str);
+                        sw.Write("</base64></root>");
+                    }
 
-                    XmlReader DataReader = GetReader(fileName);
+                    FilePathUtil.addStream(fileName, ms);
+
+                    using XmlReader DataReader = GetReader(fileName);
 
                     int SIZE = (totalfilesize - 30);
                     int SIZE64 = SIZE * 3 / 4;
@@ -974,8 +980,6 @@ public void ReadBase64DoesNotRunIntoOverflow2()
                     readSize = 0;
                     currentSize = DataReader.ReadElementContentAsBase64(base64, startPos, readSize);
                     TestLog.Compare(currentSize, 0, "Read other than Zero Bytes");
-
-                    DataReader.Dispose();
                 }
 
                 //[Variation("SubtreeReader inserted attributes don't work with ReadContentAsBase64")]