test: refactor test-file-write-stream3

* use common.mustCall() to verify all tests have run
* eliminate unneeded removeTestFile()
* eliminate unneeded var leaking into global scope
* var -> const
* remove instance of let
PR-URL: #6050
Reviewed-By: James M Snell <jasnell@gmail.com>

Author: Trott

test/parallel/test-file-write-stream3.js

@@ -5,21 +5,20 @@ const path = require('path');
 constfs=require('fs');
 
 
-varfilepath=path.join(common.tmpDir,'write_pos.txt');
+constfilepath=path.join(common.tmpDir,'write_pos.txt');
 
 
 constcb_expected='write open close write open close write open close ';
-letcb_occurred='';
+varcb_occurred='';
 
-varfileDataInitial='abcdefghijklmnopqrstuvwxyz';
+constfileDataInitial='abcdefghijklmnopqrstuvwxyz';
 
-varfileDataExpected_1='abcdefghijklmnopqrstuvwxyz';
-varfileDataExpected_2='abcdefghij123456qrstuvwxyz';
-varfileDataExpected_3='abcdefghij\u2026\u2026qrstuvwxyz';
+constfileDataExpected_1='abcdefghijklmnopqrstuvwxyz';
+constfileDataExpected_2='abcdefghij123456qrstuvwxyz';
+constfileDataExpected_3='abcdefghij\u2026\u2026qrstuvwxyz';
 
 
 process.on('exit',function(){
-removeTestFile();
 if(cb_occurred!==cb_expected){
 console.log(' Test callback events missing or out of order:');
 console.log(' expected: %j',cb_expected);
@@ -30,12 +29,6 @@ process.on('exit', function() {
 }
 });
 
-functionremoveTestFile(){
-try{
-fs.unlinkSync(filepath);
-}catch(ex){}
-}
-
 
 common.refreshTmpDir();
 
@@ -164,20 +157,14 @@ function run_test_3() {
 }
 
 
-functionrun_test_4(){
-varoptions;
-
-options={start: -5,
-flags: 'r+'};
-
+construn_test_4=common.mustCall(function(){
 // Error: start must be >= zero
 assert.throws(
 function(){
-file=fs.createWriteStream(filepath,options);
+fs.createWriteStream(filepath,{start: -5,flags: 'r+'});
 },
 /startmustbe/
 );
-
-}
+});
 
 run_test_1();