test: use fs.copyFileSync()

Use the potentially more efficient fs.copyFileSync() instead of reading
the whole file in and writing the whole file out in JavaScript.

PR-URL: #20340
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>
Reviewed-By: Khaidi Chu <i@2333.moe>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

test/parallel/test-child-process-fork-exec-path.js

@@ -23,6 +23,7 @@
 const common = require('../common');
 const assert = require('assert');
 const fs = require('fs');
+const { COPYFILE_FICLONE } = fs.constants;
 const path = require('path');
 const tmpdir = require('../common/tmpdir');
 const msg = { test: 'this' };
@@ -44,7 +45,7 @@ if (process.env.FORK) {
  } catch (e) {
  if (e.code !== 'ENOENT') throw e;
  }
- fs.writeFileSync(copyPath, fs.readFileSync(nodePath));
+ fs.copyFileSync(nodePath, copyPath, COPYFILE_FICLONE);
  fs.chmodSync(copyPath, '0755');
 
  // slow but simple

test/parallel/test-module-loading-globalpaths.js

@@ -4,6 +4,7 @@ const fixtures = require('../common/fixtures');
 const assert = require('assert');
 const path = require('path');
 const fs = require('fs');
+const { COPYFILE_FICLONE } = fs.constants;
 const child_process = require('child_process');
 const pkgName = 'foo';
 const { addLibraryPath } = require('../common/shared-lib-util');
@@ -28,7 +29,7 @@ if (process.argv[2] === 'child') {
  testExecPath = path.join(prefixBinPath, path.basename(process.execPath));
  }
  const mode = fs.statSync(process.execPath).mode;
- fs.writeFileSync(testExecPath, fs.readFileSync(process.execPath));
+ fs.copyFileSync(process.execPath, testExecPath, COPYFILE_FICLONE);
  fs.chmodSync(testExecPath, mode);
 
  const runTest = (expectedString, env) => {