ran npm run tdd

test/factorial/factorial.js

@@ -1,6 +1,7 @@
-module.exports = factorial = n =>
+const factorial = n =>
 n < 0
 ? (() => {
 throw new TypeError('Negative numbers are not allowed!');
 })()
-: n <= 1 ? 1 : n * factorial(n - 1);
+: n <= 1 ? 1 : n * factorial(n - 1);
+ module.exports = factorial