Whenever I execute any test case in Attribute Services/Attribute Write Values
the CTT leaks one session, which makes the Nano embedded UA server fail
to accept additional sessions in subsequent scripts.

I tried this modified script, and it seems to work:

--- "maintree/Attribute Services/Attribute Write Values/Test Cases/initialize.js" 2018-11-06 18:09:42.000000000 +0100
+++ initialize.js 2018-11-09 10:53:18.066432470 +0100
@@ -6,11 +6,11 @@

addLog( "TESTING AN -- OPTIONAL -- CONFORMANCE UNIT" );

-// read the original values of all scalar types, because we will revert to their original values at the end of the test
-var originalScalarValues = MonitoredItem.fromSettings( Settings.ServerTest.NodeIds.Static.AllProfiles.Scalar.Settings );
-if( originalScalarValues !== null && originalScalarValues.length !== 0 ) {

• if( !Test.Connect() ) stopCurrentUnit();
• else {
  +if( !Test.Connect() ) stopCurrentUnit();
  +else {
• // read the original values of all scalar types, because we will revert to their original values at the end of the test
• var originalScalarValues = MonitoredItem.fromSettings( Settings.ServerTest.NodeIds.Static.AllProfiles.Scalar.Settings );
• if( originalScalarValues !== null && originalScalarValues.length !== 0 ) {
  if( !ReadHelper.Execute( { NodesToRead: originalScalarValues } ) ) {
  addError( "Unable to read the initial values of the test nodes. Aborting testing." );
  stopCurrentUnit();
  @@ -20,13 +20,10 @@
  Test.PostTestFunctions.push( revertToOriginalValues );
  }
  }
  -}

-// read the original values of all array types, because we will revert to their original values at the end of the test
-var originalArrayValues = MonitoredItem.fromSettings(Settings.ServerTest.NodeIds.Static.AllProfiles.Arrays.Settings);
-if ( originalArrayValues !== null && originalArrayValues.length !== 0 ) {

• if ( !Test.Connect() ) stopCurrentUnit();
• else {
• // read the original values of all array types, because we will revert to their original values at the end of the test
• var originalArrayValues = MonitoredItem.fromSettings(Settings.ServerTest.NodeIds.Static.AllProfiles.Arrays.Settings);
• if ( originalArrayValues !== null && originalArrayValues.length !== 0 ) {
  if (!ReadHelper.Execute( { NodesToRead: originalArrayValues } ) ) {
  addError( "Unable to read the initial values of the test nodes. Aborting testing." );
  stopCurrentUnit();