Grunt: Test that package.json dependencies were installed correctly.

deps.js

grunt.registerTask('deps', 'Test that package.json dependencies were installed correctly.', function() {
  var pkg = grunt.file.readJSON('package.json');
  var total = 0;

  ['dependencies', 'devDependencies'].forEach(function(key) {
    var deps = pkg[key];
    if (!deps) { return; }
    grunt.verbose.subhead(key);
    Object.keys(deps).forEach(function(name) {
      total++;
      var msg = 'Checking "' + name + '" dependency...';
      grunt.verbose.write(msg);
      try {
        require(name);
        grunt.verbose.ok();
      } catch(err) {
        grunt.verbose.or.write(msg);
        grunt.log.error().error(err.message);
      }
    });
  });

  if (this.errorCount > 0) {
    grunt.fail.fatal('Errors were encountered. Did you "npm install" first?');
  } else {
    grunt.verbose.writeln();
    grunt.log.ok(total + ' dependencies installed correctly.');
  }
});

My grunt-check-modules task just delegates to npm ls and checks for an error exit code. Though this is an interesting idea, since npm ls has some bugs.