test: improve code in test-fs-readfile-error

* use const instead of var
* use common.mustCall to control the functions execution automatically
* use assert.strictEqual instead of assert.equal
* use assert.notStrictEqual instead of assert.notEqual
* use arrow functions
PR-URL: #10367
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

Author: edsadr

test/parallel/test-fs-readfile-error.js

@@ -1,8 +1,8 @@
 'use strict';
-varcommon=require('../common');
-varassert=require('assert');
-varexec=require('child_process').exec;
-varpath=require('path');
+constcommon=require('../common');
+constassert=require('assert');
+constexec=require('child_process').exec;
+constpath=require('path');
 
 // `fs.readFile('/')` does not fail on FreeBSD, because you can open and read
 // the directory there.
@@ -12,23 +12,23 @@ if (process.platform === 'freebsd') {
 }
 
 functiontest(env,cb){
-varfilename=path.join(common.fixturesDir,'test-fs-readfile-error.js');
-varexecPath='"'+process.execPath+'" "'+filename+'"';
-varoptions={env: Object.assign(process.env,env)};
-exec(execPath,options,function(err,stdout,stderr){
+constfilename=path.join(common.fixturesDir,'test-fs-readfile-error.js');
+constexecPath='"'+process.execPath+'" "'+filename+'"';
+constoptions={env: Object.assign(process.env,env)};
+exec(execPath,options,common.mustCall((err,stdout,stderr)=>{
 assert(err);
-assert.equal(stdout,'');
-assert.notEqual(stderr,'');
+assert.strictEqual(stdout,'');
+assert.notStrictEqual(stderr,'');
 cb(''+stderr);
-});
+}));
 }
 
-test({NODE_DEBUG: ''},common.mustCall(function(data){
+test({NODE_DEBUG: ''},common.mustCall((data)=>{
 assert(/EISDIR/.test(data));
 assert(!/test-fs-readfile-error/.test(data));
 }));
 
-test({NODE_DEBUG: 'fs'},common.mustCall(function(data){
+test({NODE_DEBUG: 'fs'},common.mustCall((data)=>{
 assert(/EISDIR/.test(data));
 assert(/test-fs-readfile-error/.test(data));
 }));