diff --git a/tests/spec/fs.appendFile.spec.js b/tests/spec/fs.appendFile.spec.js
index 480eaed..596b20d 100644
--- a/tests/spec/fs.appendFile.spec.js
+++ b/tests/spec/fs.appendFile.spec.js
@@ -1,12 +1,14 @@
-var util = require('../lib/test-utils.js');
-var expect = require('chai').expect;
+'use strict';
+
+const util = require('../lib/test-utils.js');
+const expect = require('chai').expect;
 
 describe('fs.appendFile', function() {
   const contents = 'This is a file.';
 
   beforeEach(function(done) {
     util.setup(function() {
-      var fs = util.fs();
+      const fs = util.fs();
       fs.writeFile('/myfile', contents, function(error) {
         if(error) throw error;
         done();
@@ -16,13 +18,13 @@ describe('fs.appendFile', function() {
   afterEach(util.cleanup);
 
   it('should be a function', function() {
-    var fs = util.fs();
+    const fs = util.fs();
     expect(fs.appendFile).to.be.a('function');
   });
 
   it('should append a utf8 file without specifying utf8 in appendFile', function(done) {
-    var fs = util.fs();
-    var more = ' Appended.';
+    const fs = util.fs();
+    const more = ' Appended.';
 
     fs.appendFile('/myfile', more, function(error) {
       if(error) throw error;
@@ -36,8 +38,8 @@ describe('fs.appendFile', function() {
   });
 
   it('should append a utf8 file with "utf8" option to appendFile', function(done) {
-    var fs = util.fs();
-    var more = ' Appended.';
+    const fs = util.fs();
+    const more = ' Appended.';
 
     fs.appendFile('/myfile', more, 'utf8', function(error) {
       if(error) throw error;
@@ -51,8 +53,8 @@ describe('fs.appendFile', function() {
   });
 
   it('should append a utf8 file with {encoding: "utf8"} option to appendFile', function(done) {
-    var fs = util.fs();
-    var more = ' Appended.';
+    const fs = util.fs();
+    const more = ' Appended.';
 
     fs.appendFile('/myfile', more, { encoding: 'utf8' }, function(error) {
       if(error) throw error;
@@ -66,12 +68,12 @@ describe('fs.appendFile', function() {
   });
 
   it('should append a binary file', function(done) {
-    var fs = util.fs();
+    const fs = util.fs();
 
     // String and utf8 binary encoded versions of the same thing: 'This is a file.'
-    var binary = Buffer.from([84, 104, 105, 115, 32, 105, 115, 32, 97, 32, 102, 105, 108, 101, 46]);
-    var binary2 = Buffer.from([32, 65, 112, 112, 101, 110, 100, 101, 100, 46]);
-    var binary3 = Buffer.from([84, 104, 105, 115, 32, 105, 115, 32, 97, 32, 102, 105, 108, 101, 46,
+    const binary = Buffer.from([84, 104, 105, 115, 32, 105, 115, 32, 97, 32, 102, 105, 108, 101, 46]);
+    const binary2 = Buffer.from([32, 65, 112, 112, 101, 110, 100, 101, 100, 46]);
+    const binary3 = Buffer.from([84, 104, 105, 115, 32, 105, 115, 32, 97, 32, 102, 105, 108, 101, 46,
       32, 65, 112, 112, 101, 110, 100, 101, 100, 46]);
 
     fs.writeFile('/mybinaryfile', binary, function(error) {
@@ -90,9 +92,9 @@ describe('fs.appendFile', function() {
   });
 
   it('should follow symbolic links', function(done) {
-    var fs = util.fs();
-    var contents = 'This is a file.';
-    var more = ' Appended.';
+    const fs = util.fs();
+    const contents = 'This is a file.';
+    const more = ' Appended.';
 
     fs.symlink('/myfile', '/myFileLink', function (error) {
       if (error) throw error;
@@ -110,7 +112,7 @@ describe('fs.appendFile', function() {
   });
 
   it('should work when file does not exist, and create the file', function(done) {
-    var fs = util.fs();
+    const fs = util.fs();
 
     fs.appendFile('/newfile', contents, { encoding: 'utf8' }, function(error) {
       expect(error).not.to.exist;
@@ -124,8 +126,8 @@ describe('fs.appendFile', function() {
   });
   
   it('should accept numbers and append them to the file', function(done) {
-    var fs = util.fs();
-    var more = 10000;
+    const fs = util.fs();
+    const more = 10000;
 
     fs.appendFile('/myfile', more, 'utf8', function(error) {
       if(error) throw error;
@@ -142,7 +144,7 @@ describe('fs.appendFile', function() {
 describe('fs.promises.appendFile', function() {
   beforeEach(function(done) {
     util.setup(function() {
-      var fs = util.fs();
+      const fs = util.fs();
       return fs.promises.writeFile('/myfile', 'This is a file.', { encoding: 'utf8' })
         .then(done)
         .catch(done);
@@ -151,14 +153,14 @@ describe('fs.promises.appendFile', function() {
   afterEach(util.cleanup);
 
   it('should be a function', function() {
-    var fs = util.fs();
+    const fs = util.fs();
     expect(fs.promises.appendFile).to.be.a('function');
   });
 
   it('should append a utf8 file without specifying utf8 in appendFile', function() {
-    var fs = util.fs();
-    var contents = 'This is a file.';
-    var more = ' Appended.';
+    const fs = util.fs();
+    const contents = 'This is a file.';
+    const more = ' Appended.';
 
     return fs.promises.appendFile('/myfile', more)
       .then(() => fs.promises.readFile('/myfile', 'utf8'))
@@ -166,9 +168,9 @@ describe('fs.promises.appendFile', function() {
   });
 
   it('should append a utf8 file with "utf8" option to appendFile', function() {
-    var fs = util.fs();
-    var contents = 'This is a file.';
-    var more = ' Appended.';
+    const fs = util.fs();
+    const contents = 'This is a file.';
+    const more = ' Appended.';
 
     return fs.promises.appendFile('/myfile', more, 'utf8')
       .then(() => fs.promises.readFile('/myfile', 'utf8'))
@@ -176,9 +178,9 @@ describe('fs.promises.appendFile', function() {
   });
 
   it('should append a utf8 file with {encoding: "utf8"} option to appendFile', function() {
-    var fs = util.fs();
-    var contents = 'This is a file.';
-    var more = ' Appended.';
+    const fs = util.fs();
+    const contents = 'This is a file.';
+    const more = ' Appended.';
 
     return fs.promises.appendFile('/myfile', more, { encoding: 'utf8' })
       .then(() => fs.promises.readFile('/myfile', { encoding: 'utf8' }))
@@ -186,12 +188,12 @@ describe('fs.promises.appendFile', function() {
   });
 
   it('should append a binary file', function() {
-    var fs = util.fs();
+    const fs = util.fs();
 
     // String and utf8 binary encoded versions of the same thing: 'This is a file.'
-    var binary = new Buffer([84, 104, 105, 115, 32, 105, 115, 32, 97, 32, 102, 105, 108, 101, 46]);
-    var binary2 = new Buffer([32, 65, 112, 112, 101, 110, 100, 101, 100, 46]);
-    var binary3 = new Buffer([84, 104, 105, 115, 32, 105, 115, 32, 97, 32, 102, 105, 108, 101, 46,
+    const binary = new Buffer([84, 104, 105, 115, 32, 105, 115, 32, 97, 32, 102, 105, 108, 101, 46]);
+    const binary2 = new Buffer([32, 65, 112, 112, 101, 110, 100, 101, 100, 46]);
+    const binary3 = new Buffer([84, 104, 105, 115, 32, 105, 115, 32, 97, 32, 102, 105, 108, 101, 46,
       32, 65, 112, 112, 101, 110, 100, 101, 100, 46]);
 
     return fs.promises.writeFile('/mybinaryfile', binary)
@@ -201,9 +203,9 @@ describe('fs.promises.appendFile', function() {
   });
 
   it('should follow symbolic links', function() {
-    var fs = util.fs();
-    var contents = 'This is a file.';
-    var more = ' Appended.';
+    const fs = util.fs();
+    const contents = 'This is a file.';
+    const more = ' Appended.';
 
     return fs.promises.symlink('/myfile', '/myFileLink')
       .then(() => fs.promises.appendFile('/myFileLink', more, 'utf8'))
@@ -212,8 +214,8 @@ describe('fs.promises.appendFile', function() {
   });
 
   it('should work when file does not exist, and create the file', function() {
-    var fs = util.fs();
-    var contents = 'This is a file.';
+    const fs = util.fs();
+    const contents = 'This is a file.';
 
     return fs.promises.appendFile('/newfile', contents, { encoding: 'utf8' })
       .then(() => fs.promises.readFile('/newfile', 'utf8'))