feat(randomInteger): Add randomInteger with tests

To close #13 , I add a function that return an integer between min and max input. The test make sure
that the result won't be lower than min input and won't be greater than max input.

#13

Author: lukyth

src/index.js

@@ -2,12 +2,13 @@ import flatten from './flatten'
 import getQueryStringParam from './get-query-string-param'
 import snakeToCamel from './snake-to-camel'
 import padLeft from './pad-left'
+import randomInteger from './random-integer'
 
 
 export {
   flatten,
   snakeToCamel,
   getQueryStringParam,
   padLeft,
+  randomInteger,
 }
-

src/random-integer.js

@@ -0,0 +1,15 @@
+export default randomInteger
+
+/**
+ * Original Source: http://stackoverflow.com/a/24152886
+ *
+ * This method will return a random integer
+ * between min and max number
+ *
+ * @param {Number} min - The minimum number to be random
+ * @param {Number} max - The maximum number to be random
+ * @return {Number} A random integer between min and max
+ */
+function randomInteger(min, max) {
+  return Math.floor(Math.random() * (max - min + 1)) + min
+}

test/random-integer.test.js

@@ -0,0 +1,16 @@
+import test from 'ava'
+import {randomInteger} from '../src'
+
+test('result shouldn\'t be lower than min number', t => {
+  const min = 1
+  const max = 10
+  const result = randomInteger(min, max)
+  t.false(result < min)
+})
+
+test('result shouldn\'t be greater than max number', t => {
+  const min = 1
+  const max = 10
+  const result = randomInteger(min, max)
+  t.false(result > max)
+})