ran npm run tdd

test/standardDeviation/standardDeviation.js

@@ -1,7 +1,8 @@
-module.exports = standardDeviation = (arr, usePopulation = false) => {
+const standardDeviation = (arr, usePopulation = false) => {
 const mean = arr.reduce((acc, val) => acc + val, 0) / arr.length;
 return Math.sqrt(
 arr.reduce((acc, val) => acc.concat((val - mean) ** 2), []).reduce((acc, val) => acc + val, 0) /
 (arr.length - (usePopulation ? 0 : 1))
 );
-};
+};
+ module.exports = standardDeviation