Use yarn and in addition also build the project

Author: dweber019

appveyor.yml

@@ -1,21 +1,12 @@
-# Test against the latest version of this Node.js version
 environment:
   nodejs_version: "7"
 
-# Install scripts. (runs after repo cloning)
 install:
-  # Get the latest stable version of Node.js or io.js
   - ps: Install-Product node $env:nodejs_version
-  # install modules
-  - npm install
+  - yarn install
+
+build_script:
+  - npm run build
 
-# Post-install test scripts.
 test_script:
-  # Output useful info for debugging.
-  - node --version
-  - npm --version
-  # run tests
   - npm test
-
-# Don't actually build.
-build: off