Add initial scaffold test (#7)

Add an initial integration test that will scaffold the app and run yarn targets from within that app.

.gitignore

@@ -1,2 +1,3 @@
 node_modules/
 yarn-error.log
+test-artifacts/

package.json

@@ -25,8 +25,9 @@
     "prettier": "^1.13.5"
   },
   "scripts": {
+    "clean": "rm -rf test-artifacts",
     "lint": "eslint .",
-    "test": "jest"
+    "test": "yarn clean && jest"
   },
   "jest": {
     "cache": false,

tests/test.js

@@ -1,4 +1,24 @@
 // @flow
 /* eslint-env jest */
 
-test('able to create an app', () => {});
+const {promisify} = require('util');
+const exec = promisify(require('child_process').exec);
+
+function log(execOutput) {
+  // eslint-disable-next-line no-console
+  console.log(execOutput.stdout);
+}
+
+test(
+  'scaffolded app tests pass',
+  async () => {
+    await exec(`mkdir test-artifacts`);
+    log(
+      await exec(`node ../bin/cli.js test-scaffold`, {cwd: './test-artifacts'})
+    );
+
+    const options = {cwd: './test-artifacts/test-scaffold'};
+    log(await exec(`yarn build`, options));
+  },
+  300000
+);