diff --git a/__tests__/.eslintrc.json b/__tests__/.eslintrc.json
new file mode 100644
index 0000000..55f121d
--- /dev/null
+++ b/__tests__/.eslintrc.json
@@ -0,0 +1,5 @@
+{
+  "env": {
+    "jest": true
+  }
+}
diff --git a/__tests__/prerender.test.js b/__tests__/prerender.test.js
new file mode 100644
index 0000000..5f1cc25
--- /dev/null
+++ b/__tests__/prerender.test.js
@@ -0,0 +1,7 @@
+const render = require('../index');
+
+describe('Pre-renderer', () => {
+  it('pre-renders a web page', () => {
+    return expect(render('https://google.com')).resolves.toMatch(/google/i);
+  });
+});
diff --git a/index.js b/index.js
index fde4dc2..929d845 100644
--- a/index.js
+++ b/index.js
@@ -26,7 +26,7 @@ module.exports = function (source, chromeFlags) {
       () => chrome.kill()
     );
   })
-  .then((results) => results.find(r => r.extractedHTML).extractedHTML);
+  .then((results) => results.find(r => r && r.extractedHTML).extractedHTML);
 }
 
 function extractHtml(evaluatedCode) {
@@ -34,12 +34,12 @@ function extractHtml(evaluatedCode) {
 }
 
 function launchChrome(url, flags) {
-  debug('Launching Chrome headless');
+  debug('Launching Chrome headless for url "%s"', url);
   const chromeFlags = [
     '--disable-gpu',
     '--headless',
-  ].concat(flags);
-  debug('Chrome flags: %s', chromeFlags.join(' '));
+  ].concat(flags).filter(Boolean);
+  debug('Chrome flags: %s', chromeFlags);
 
   return chromeLauncher.launch({
     startingUrl: url,
diff --git a/package.json b/package.json
index 20894cb..fd09357 100644
--- a/package.json
+++ b/package.json
@@ -17,7 +17,8 @@
   },
   "scripts": {
     "lint": "eslint index.js",
-    "test": "jest"
+    "test": "jest",
+    "test:watch": "DEBUG=prerender jest --watchAll"
   },
   "dependencies": {
     "chrome-launcher": "^0.2.1",