Conditionally load polyfills required for testing

Author: lukechilds

package.json

@@ -23,6 +23,7 @@
     "@babel/core": "^7.4.4",
     "@babel/preset-env": "^7.4.4",
     "airtap": "^2.0.2",
+    "core-js": "^3.0.1",
     "cross-env": "^5.2.0",
     "object.getownpropertydescriptors": "^2.0.3",
     "tape": "^4.10.1"

test.js

@@ -1,5 +1,11 @@
 const test = require('tape');
 
+// Conditionally load polyfills required for testing
+if (typeof Promise === 'undefined') {
+  console.log('Loading Promise polyfill');
+  require('core-js/features/promise');
+}
+
 const testPaths = [
   ['test-assert-async.js', () => require('./test/parallel/test-assert-async.js')],
   ['test-assert-checktag.js', () => require('./test/parallel/test-assert-checktag.js')],