Fix yarnInstall to add new package - Fix #980

lib/actions/install.js

@@ -35,6 +35,11 @@ install.runInstall = function (installer, paths, options, cb) {
 
   var args = ['install'].concat(paths).concat(dargs(options));
 
+  // Yarn uses the `add` command to specifically add a package to a project.
+  if (installer === 'yarn' && paths.length > 0) {
+    args[0] = 'add';
+  }
+
   // only for npm, use a minimum cache of one day
   if (installer === 'npm') {
     args = args.concat(['--cache-min', 24 * 60 * 60]);
@@ -49,7 +54,7 @@ install.runInstall = function (installer, paths, options, cb) {
   this.env.runLoop.add('install', function (done) {
     this.emit(installer + 'Install', paths);
     this.spawnCommand(installer, args, options)
-      .on('error', function (err){
+      .on('error', function (err) {
         console.log(chalk.red('Could not finish installation. \n') +
           'Please install ' + installer + ' with ' +
           chalk.yellow('npm install -g ' + installer) + ' and try again.'

test/install.js

@@ -164,16 +164,18 @@ describe('Base (actions/install mixin)', function () {
     });
 
     it('run without callback', function (done) {
-      this.dummy.yarnInstall('yo', { save: true });
+      this.dummy.yarnInstall('yo', {dev: true});
       this.dummy.run(function () {
         sinon.assert.calledOnce(this.spawnCommandStub);
+        sinon.assert.calledWithExactly(this.spawnCommandStub, 'yarn', ['add', 'yo', '--dev'], {dev: true});
         done();
       }.bind(this));
     });
 
     it('run with callback', function (done) {
-      this.dummy.yarnInstall('yo', { save: true }, function () {
+      this.dummy.yarnInstall('yo', function () {
         sinon.assert.calledOnce(this.spawnCommandStub);
+        sinon.assert.calledWithExactly(this.spawnCommandStub, 'yarn', ['add', 'yo'], {});
         done();
       }.bind(this));
       this.dummy.run();