test(transactions): ensure lsids are saved before cleanup

This modifies the test runner to run to spec by saving off the
session ids when they are created so that they can be used to check
expectations after cleanup. With the changes introduced in the core
component to this PR the id's are actually explicitly reset when
`endSession` is called, so the test was succeeding by side effect
previously.

test/functional/transactions_tests.js

@@ -403,7 +403,16 @@ function runTestSuiteTest(configuration, spec, context) {
     // enable to see useful APM debug information at the time of actual test run
     // displayCommands = true;
 
-    const operationContext = { database, session0, session1, testRunner: context };
+    const operationContext = {
+      database,
+      session0,
+      session1,
+      testRunner: context,
+      savedSessionData: {
+        session0: JSON.parse(EJSON.stringify(session0.id)),
+        session1: JSON.parse(EJSON.stringify(session1.id))
+      }
+    };
 
     let testPromise = Promise.resolve();
     return testPromise
@@ -440,13 +449,10 @@ function validateOutcome(testData, testContext) {
 }
 
 function validateExpectations(commandEvents, spec, testContext, operationContext) {
-  const session0 = operationContext.session0;
-  const session1 = operationContext.session1;
-
   if (spec.expectations && Array.isArray(spec.expectations) && spec.expectations.length > 0) {
     const actualEvents = normalizeCommandShapes(commandEvents);
     const rawExpectedEvents = spec.expectations.map(x =>
-      linkSessionData(x.command_started_event, { session0, session1 })
+      linkSessionData(x.command_started_event, operationContext.savedSessionData)
     );
 
     const expectedEventPlaceholders = rawExpectedEvents.map(event =>
@@ -496,9 +502,8 @@ function validateExpectations(commandEvents, spec, testContext, operationContext
 }
 
 function linkSessionData(command, context) {
-  const session = context[command.command.lsid];
   const result = Object.assign({}, command);
-  result.command.lsid = JSON.parse(EJSON.stringify(session.id));
+  result.command.lsid = context[command.command.lsid];
   return result;
 }