test: test syncrhnous methods of child_process in snapshot

These currently work in snapshot builder scripts. Asynchronous
methods are not supported yet.

PR-URL: https://github.com/nodejs/node/pull/50943
Refs: https://github.com/nodejs/node/issues/50924
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

test/fixtures/snapshot/child-process-sync.js

@@ -0,0 +1,25 @@
+'use strict';
+
+const {
+  setDeserializeMainFunction,
+  isBuildingSnapshot
+} = require('v8').startupSnapshot;
+
+function spawn() {
+  const { spawnSync, execFileSync, execSync } = require('child_process');
+  spawnSync(process.execPath, [ __filename, 'spawnSync' ], { stdio: 'inherit' });
+  execSync(`"${process.execPath}" "${__filename}" "execSync"`, { stdio: 'inherit' });
+  execFileSync(process.execPath, [ __filename, 'execFileSync' ], { stdio: 'inherit' });
+}
+
+if (process.argv[2] !== undefined) {
+  console.log('From child process', process.argv[2]);
+} else {
+  spawn();
+}
+
+if (isBuildingSnapshot()) {
+  setDeserializeMainFunction(() => {
+    spawn();
+  });
+}

test/parallel/test-snapshot-child-process-sync.js

@@ -0,0 +1,53 @@
+'use strict';
+
+// This tests that process.cwd() is accurate when
+// restoring state from a snapshot
+
+require('../common');
+const { spawnSyncAndExitWithoutError } = require('../common/child_process');
+const tmpdir = require('../common/tmpdir');
+const fixtures = require('../common/fixtures');
+const assert = require('assert');
+
+tmpdir.refresh();
+const blobPath = tmpdir.resolve('snapshot.blob');
+const file = fixtures.path('snapshot', 'child-process-sync.js');
+const expected = [
+  'From child process spawnSync',
+  'From child process execSync',
+  'From child process execFileSync',
+];
+
+{
+  // Create the snapshot.
+  spawnSyncAndExitWithoutError(process.execPath, [
+    '--snapshot-blob',
+    blobPath,
+    '--build-snapshot',
+    file,
+  ], {
+    cwd: tmpdir.path,
+  }, {
+    trim: true,
+    stdout(output) {
+      assert.deepStrictEqual(output.split('\n'), expected);
+      return true;
+    }
+  });
+}
+
+{
+  spawnSyncAndExitWithoutError(process.execPath, [
+    '--snapshot-blob',
+    blobPath,
+    file,
+  ], {
+    cwd: tmpdir.path,
+  }, {
+    trim: true,
+    stdout(output) {
+      assert.deepStrictEqual(output.split('\n'), expected);
+      return true;
+    }
+  });
+}