Add an algorithm to find mean absolute deviation (#1165)

Maths/test/MeanAbsoluteDeviation.test.js

@@ -0,0 +1,16 @@
+import { meanAbsoluteDeviation } from '../MeanAbsoluteDeviation.js'
+
+describe('tests for mean absolute deviation', () => {
+  it('should be a function', () => {
+    expect(typeof meanAbsoluteDeviation).toEqual('function')
+  })
+
+  it('should throw an invalid input error', () => {
+    expect(() => meanAbsoluteDeviation('fgh')).toThrow()
+  })
+
+  it('should return the mean absolute devition of an array of numbers', () => {
+    const meanAbDev = meanAbsoluteDeviation([2, 34, 5, 0, -2])
+    expect(meanAbDev).toBe(10.479999999999999)
+  })
+})