diff --git a/lib/main.js b/lib/main.js
index c7de33cb..a2ef5dc4 100644
--- a/lib/main.js
+++ b/lib/main.js
@@ -95,9 +95,9 @@ Lambda.prototype._runHandler = function (handler, event, program, context) {
 
 Lambda.prototype._params = function (program, buffer) {
   var params = {
-    FunctionName: program.functionName
-      + (program.environment ? '-' + program.environment : '')
-      + (program.lambdaVersion ? '-' + program.lambdaVersion : ''),
+    FunctionName: program.functionName +
+      (program.environment ? '-' + program.environment : '') +
+      (program.lambdaVersion ? '-' + program.lambdaVersion : ''),
     Code: {
       ZipFile: buffer
     },
@@ -206,10 +206,12 @@ Lambda.prototype._fileCopy = function (program, src, dest, excludeNodeModules, c
       str = str.substr(0, str.length - 1);
       dirBlobs.push(str);
     }
-    if (str.charAt(0) === path.sep)
+    if (str.charAt(0) === path.sep) {
       return path.join(srcAbsolutePath, str);
-    if (str.indexOf(path.sep) >= 0)
+    }
+    if (str.indexOf(path.sep) >= 0) {
       return path.join(path.resolve('/**'), str);
+    }
     return str;
   }).join(',') + '}';
   const dirPatternRegExp = new RegExp(`(${dirBlobs.join('|')})$`);
@@ -226,11 +228,13 @@ Lambda.prototype._fileCopy = function (program, src, dest, excludeNodeModules, c
           return true;
         }
 
-        if (!minimatch(src, pattern, { matchBase: true }))
+        if (!minimatch(src, pattern, { matchBase: true })) {
           return true;
+        }
         // Directory check. Even if `src` is a directory it will not end with '/'.
-        if (!dirPatternRegExp.test(src))
+        if (!dirPatternRegExp.test(src)) {
           return false;
+        }
         return !fs.statSync(src).isDirectory();
       }
     };
@@ -246,8 +250,8 @@ Lambda.prototype._fileCopy = function (program, src, dest, excludeNodeModules, c
 
 // `_rsync` will be replaced by` _fileCopy`.
 Lambda.prototype._rsync = function (program, src, dest, excludeNodeModules, callback) {
-  var excludes = ['.git*', '*.swp', '.editorconfig', '.lambda', 'deploy.env', '*.log', '/build/'],
-    excludeGlobs = [];
+  var excludes = ['.git*', '*.swp', '.editorconfig', '.lambda', 'deploy.env', '*.log', '/build/'];
+  var excludeGlobs = [];
   if (program.excludeGlobs) {
     excludeGlobs = program.excludeGlobs.split(' ');
   }
@@ -286,9 +290,9 @@ Lambda.prototype._npmInstall = function (program, codeDirectory, callback) {
     `--prefix ${codeDirectory}`,
     process.platform === 'win32' ? `--cwd ${codeDirectory}` : null
   ].join(' ');
-  var command = program.dockerImage ?
-    'docker run --rm -v ' + codeDirectory + ':/var/task ' + program.dockerImage + ' npm -s install --production' :
-    `npm -s install --production ${installOptions}`;
+  var command = program.dockerImage
+    ? 'docker run --rm -v ' + codeDirectory + ':/var/task ' + program.dockerImage + ' npm -s install --production'
+    : `npm -s install --production ${installOptions}`;
   exec(command, {
     maxBuffer: maxBufferSize,
     env: process.env
@@ -317,7 +321,7 @@ Lambda.prototype._postInstallScript = function (program, codeDirectory, callback
     maxBuffer: maxBufferSize
   }, function (error, stdout, stderr) {
     if (error) {
-      return callback(error + ' stdout: ' + stdout + ' stderr: ' + stderr);
+      return callback(new Error(`${error} stdout: ${stdout} stderr: ${stderr}`));
     }
     console.log('\t\t' + stdout);
     callback(null);
@@ -438,9 +442,9 @@ Lambda.prototype._archive = function (program, archiveCallback) {
   if (program.deployZipfile && fs.existsSync(program.deployZipfile)) {
     return this._readArchive(program, archiveCallback);
   }
-  return program.prebuiltDirectory ?
-    this._archivePrebuilt(program, archiveCallback) :
-    this._buildAndArchive(program, archiveCallback);
+  return program.prebuiltDirectory
+    ? this._archivePrebuilt(program, archiveCallback)
+    : this._buildAndArchive(program, archiveCallback);
 };
 
 Lambda.prototype._archivePrebuilt = function (program, archiveCallback) {
@@ -632,13 +636,13 @@ Lambda.prototype._updateScheduleEvents = function (scheduleEvents, functionArn,
 Lambda.prototype.package = function (program) {
   var _this = this;
   if (!program.packageDirectory) {
-    throw 'packageDirectory not specified!';
+    throw new Error('packageDirectory not specified!');
   }
   try {
     var isDir = fs.lstatSync(program.packageDirectory).isDirectory();
 
     if (!isDir) {
-      throw program.packageDirectory + ' is not a directory!';
+      throw new Error(program.packageDirectory + ' is not a directory!');
     }
   } catch (err) {
     if (err.code === 'ENOENT') {
@@ -729,7 +733,7 @@ Lambda.prototype.deploy = function (program) {
               function (_callback) {
                 // Updating event source(s)
                 _this._updateEventSources(lambda, params.FunctionName, [], eventSourceList.EventSourceMappings, function (err, results) {
-                  _callback(null, results);
+                  _callback(err, results);
                 });
               },
               function (_callback) {
diff --git a/test/handler/index.js b/test/handler/index.js
index c3332d90..40a5ec96 100644
--- a/test/handler/index.js
+++ b/test/handler/index.js
@@ -5,8 +5,10 @@ exports.handler = (event, context, callback) => {
   context.callbackWaitsForEmptyEventLoop =
     !!event.callbackWaitsForEmptyEventLoop;
 
-  if (event.asyncTest)
+  if (event.asyncTest) {
     setTimeout(() => console.log('sleep 3500 msec'), 3500);
+  }
 
+  /* eslint-disable no-eval */
   eval(event.callbackCode);
 };
diff --git a/test/main.js b/test/main.js
index 7a5a7ade..603a2386 100644
--- a/test/main.js
+++ b/test/main.js
@@ -381,8 +381,9 @@ describe('lib/main', function () {
     });
     afterEach(function () {
       hook.unhook();
-      if (fs.existsSync(postInstallScriptPath))
+      if (fs.existsSync(postInstallScriptPath)) {
         fs.unlinkSync(postInstallScriptPath);
+      }
     });
 
     it('should not throw any errors if no script', function (done) {
@@ -395,7 +396,8 @@ describe('lib/main', function () {
     it('should throw any errors if script fails', function (done) {
       fs.writeFileSync(postInstallScriptPath, '___fails___');
       lambda._postInstallScript(program, codeDirectory, function (err) {
-        assert.match(err, /^Error: Command failed:/);
+        assert.instanceOf(err, Error);
+        assert.match(err.message, /^Error: Command failed:/);
         done();
       });
     });