test: add test for child_process benchmark

PR-URL: #12326
Ref: #12068
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Alexey Orlenko <eaglexrlnk@gmail.com>

benchmark/child_process/spawn-echo.js

@@ -1,15 +1,15 @@
 'use strict';
 var common = require('../common.js');
 var bench = common.createBenchmark(main, {
-  thousands: [1]
+  n: [1000]
 });
 
 var spawn = require('child_process').spawn;
 function main(conf) {
-  var len = +conf.thousands * 1000;
+  var n = +conf.n;
 
   bench.start();
-  go(len, len);
+  go(n, n);
 }
 
 function go(n, left) {

test/sequential/test-benchmark-child-process.js

@@ -0,0 +1,19 @@
+'use strict';
+
+require('../common');
+
+const assert = require('assert');
+const fork = require('child_process').fork;
+const path = require('path');
+
+const runjs = path.join(__dirname, '..', '..', 'benchmark', 'run.js');
+
+const child = fork(runjs, ['--set', 'dur=0.1',
+                           '--set', 'n=1',
+                           '--set', 'len=1',
+                           'child_process'],
+                   {env: {NODEJS_BENCHMARK_ZERO_ALLOWED: 1}});
+child.on('exit', (code, signal) => {
+  assert.strictEqual(code, 0);
+  assert.strictEqual(signal, null);
+});