test: improve worker_threads coverage

PR-URL: #41818
Refs: https://coverage.nodejs.org/coverage-7123a00b03a90862/lib/internal/worker.js.html#L412
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

Author: ErickWendel

test/parallel/test-worker-environmentdata.js

@@ -1,4 +1,5 @@
 'use strict';
+// Flags: --expose-internals
 
 require('../common');
 const{
@@ -8,6 +9,8 @@ const {
  threadId,
 }=require('worker_threads');
 
+const{ assignEnvironmentData }=require('internal/worker');
+
 const{
  deepStrictEqual,
  strictEqual,
@@ -26,6 +29,8 @@ if (!process.env.HAS_STARTED_WORKER) {
 strictEqual(getEnvironmentData('foo'),'bar');
 deepStrictEqual(getEnvironmentData('hello'),{value: 'world'});
 strictEqual(getEnvironmentData(1),undefined);
+assignEnvironmentData(undefined);// It won't setup any key.
+strictEqual(getEnvironmentData(undefined),undefined);
 
 // Recurse to make sure the environment data is inherited
 if(threadId<=2)

test/parallel/test-worker-heap-snapshot.js

@@ -0,0 +1,16 @@
+'use strict';
+
+constcommon=require('../common');
+constassert=require('assert');
+const{ Worker }=require('worker_threads');
+const{ once }=require('events');
+
+// Ensure that worker.getHeapSnapshot() returns a valid JSON
+(async()=>{
+constworker=newWorker('setInterval(() => {}, 1000);',{eval: true});
+awaitonce(worker,'online');
+conststream=awaitworker.getHeapSnapshot();
+assert.ok(JSON.parse(stream.read()));
+
+awaitworker.terminate();
+})().then(common.mustCall());