SERVER-43973 Use a unique test name for each thread in ParallelTester

Author: Robert Guo

jstests/libs/parallelTester.js

@@ -368,7 +368,13 @@ if (typeof _threadInject != "undefined") {
         for (var i in params) {
             var param = params[i];
             var test = param.shift();
-            var t = new Thread(wrapper, test, param, {TestData: TestData});
+
+            // Make a shallow copy of TestData so we can override the test name to
+            // prevent tests on different threads that to use jsTestName() as the
+            // collection name from colliding.
+            const clonedTestData = Object.assign({}, TestData);
+            clonedTestData.testName = `ParallelTesterThread${i}`;
+            var t = new Thread(wrapper, test, param, {TestData: clonedTestData});
             runners.push(t);
         }