Fix function and tests

Author: khalidbih

Sprint-1/implement/sum.js

@@ -1,4 +1,11 @@
 function sum(elements) {
+  let total = 0;
+  for (const el of elements) {
+    if (typeof el === "number") {
+      total += el;
+    }
+  }
+  return total;
 }
-
 module.exports = sum;
+

Sprint-1/implement/sum.test.js

@@ -13,24 +13,41 @@ const sum = require("./sum.js");
 // Given an empty array
 // When passed to the sum function
 // Then it should return 0
-test.todo("given an empty array, returns 0")
+test("given an empty array, returns 0", () => {
+  expect(sum([])).toBe(0);
+});
 
 // Given an array with just one number
 // When passed to the sum function
 // Then it should return that number
+test("given an array with one number, returns that number", () => {
+    expect(sum([7])).toBe(7);
+});
 
 // Given an array containing negative numbers
 // When passed to the sum function
 // Then it should still return the correct total sum
+test("given an array containing negative numbers, returns the correct sum", () => {
+    expect(sum([10, -5, 3, -2])).toBe(6); 
+});
 
 // Given an array with decimal/float numbers
 // When passed to the sum function
 // Then it should return the correct total sum
+test("given an array with decimal numbers, returns the correct sum", () => {
+    expect(sum([1.2, 3.5, 2.3])).toBe(7.0); 
+});
 
 // Given an array containing non-number values
 // When passed to the sum function
 // Then it should ignore the non-numerical values and return the sum of the numerical elements
+test("given an array with non-number values, returns the sum of numerical elements only", () => {
+    expect(sum([10, "hi", 5, null, 3, "hello"])).toBe(18); 
+});
 
 // Given an array with only non-number values
 // When passed to the sum function
 // Then it should return the least surprising value given how it behaves for all other inputs
+test("given an array with only non-number values, returns 0", () => {
+    expect(sum(["a", "hi", null, undefined, false])).toBe(0);
+});