added solution to tally.js

Author: Alex Jamshidi

Sprint-2/implement/tally.js

@@ -1,3 +1,12 @@
-function tally() {}
+function tally(array) {
+    if (!Array.isArray(array)) {throw new Error("Invalid array");}
+    tally = {}
+    array.forEach((item) =>{
+        if (item in tally) {tally[item] += 1}
+        else tally[item] = 1;
+    })
+    return tally
+}
 
 module.exports = tally;
+

Sprint-2/implement/tally.test.js

@@ -20,15 +20,31 @@ const tally = require("./tally.js");
 // When passed an array of items
 // Then it should return an object containing the count for each unique item
 
+describe("tally", () => {
 // Given an empty array
 // When passed to tally
 // Then it should return an empty object
-test.todo("tally on an empty array returns an empty object");
+it("tally on an empty array returns an empty object", () => {
+    const array = [];
+    expect(tally(array)).toEqual({})
+});
+
 
 // Given an array with duplicate items
 // When passed to tally
 // Then it should return counts for each unique item
+it("tally returns counts for each unique item", () => {
+    const array = ['a', 'a', 'b', 'c'];
+    expect(tally(array)).toEqual({ a : 2, b: 1, c: 1 })
+});
+
 
 // Given an invalid input like a string
 // When passed to tally
 // Then it should throw an error
+it("tally on an empty array returns an empty object", () => {
+    const array = "string";
+    expect(() => {tally(array);}).toThrow("Invalid array")
+});
+});
+