add command test, fix relative paths

test/command/hello.js

+dart_library.library('hello', null, /* Imports */[
+  'dart_sdk'
+], function(exports, dart_sdk) {
+  'use strict';
+  const core = dart_sdk.core;
+  const dart = dart_sdk.dart;
+  const dartx = dart_sdk.dartx;
+  const hello = Object.create(null);
+  hello.main = function() {
+    return core.print('hello!');
+  };
+  dart.fn(hello.main);
+  // Exports:
+  exports.hello = hello;
+});
+
+//# sourceMappingURL=hello.js.map