Add a spy to track calling Parser._parseBrowser when Parser.getBrowser called

test/unit/parser.js

@@ -1,4 +1,5 @@
 import test from 'ava';
+import sinon from 'sinon';
 import Parser from '../../src/parser';
 
 const UA = 'Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_4) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/56.0.2924.87 Safari/537.36 OPR/43.0.2442.1165';
@@ -17,7 +18,9 @@ test('test', t => {
 });
 
 test('_parseBrowser', t => {
-  const b = parser._parseBrowser();
+  const spy = sinon.spy(parser, '_parseBrowser');
+  const b = parser.getBrowser();
+  t.truthy(spy.called);
   t.is(b.name, 'Opera');
   t.is(b.version, '43.0.2442.1165');
 });