Added allEqual + tests

snippets/allEqual.md

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+### allEqual
+
+Check if all elements are equal
+
+Use `Array.every()` to check if all the elements of the array are the same as the first one.
+
+```js
+const allEqual = arr => arr.every(val => val === arr[0]);
+```
+
+```js
+allEqual([1, 2, 3, 4, 5, 6]); // false
+allEqual([1, 1, 1, 1]); // true
+```

test/allEqual/allEqual.js

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+const allEqual = arr => arr.every(val => val === arr[0]);
+module.exports = allEqual;

test/allEqual/allEqual.test.js

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+const expect = require('expect');
+const allEqual = require('./allEqual.js');
+
+test('allEqual is a Function', () => {
+  expect(allEqual).toBeInstanceOf(Function);
+});
+
+test('Truthy numbers', () => {
+  expect(allEqual([4, 4, 4])).toBeTruthy();
+});
+
+test('Falsy numbers', () => {
+  expect(allEqual([4, 3.999, 4])).toBeFalsy();
+});
+
+test('Truthy strings', () => {
+  expect(allEqual(['lorem', 'lorem', 'lorem'])).toBeTruthy();
+});
+
+test('Falsy numbers', () => {
+  expect(allEqual(['lorem', 'ipsum', 'dolore'])).toBeFalsy();
+});
+
+test('Truthy trues', () => {
+  expect(allEqual([true, true, true])).toBeTruthy();
+});
+
+test('Truthy falses', () => {
+  expect(allEqual([false, false, false])).toBeTruthy();
+});
+
+test('Falsy trues', () => {
+  expect(allEqual([true, true, false])).toBeFalsy();
+});
+
+test('Falsy falses', () => {
+  expect(allEqual([false, false, true])).toBeFalsy();
+});