added screenshot of Jest tests

Author: ww9

README.md

@@ -9,3 +9,6 @@ Written in TypeScript with Jest tests in a Test Driven Development approach.
 After cloning this repo, run `npm i` to install dependencies.
 
 Then run `npm run tdd` to automatically run tests when a file changes.
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+![image](https://user-images.githubusercontent.com/27555162/144350170-1c1418e3-8932-460f-adb6-4ad0b6bbb6f6.png)
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