Swap subSeconds for addSeconds

test/expired.in.js

@@ -1,6 +1,6 @@
 import test from 'ava';
 import tk from 'timekeeper';
-import subSeconds from 'date-fns/sub_seconds';
+import addSeconds from 'date-fns/add_seconds';
 import expired from '../';
 
 test('expired.in is a function', t => {
@@ -38,14 +38,14 @@ test('expired.in returns zero ms for instantly stale cache', t => {
 
 test('expired.in returns negative ms for stale cache', t => {
 	const date = new Date().toUTCString();
-	const dateOffset = 600;
+	const dateOffset = -600;
 	const maxAge = 300;
 	const headers = {
-		date: subSeconds(date, dateOffset).toUTCString(),
+		date: addSeconds(date, dateOffset).toUTCString(),
 		age: 0,
 		'cache-control': `public, max-age=${maxAge}`
 	};
-	const expiredIn = (maxAge - dateOffset) * 1000;
+	const expiredIn = (maxAge + dateOffset) * 1000;
 
 	tk.freeze(date);
 	t.is(expired.in(headers), expiredIn);