Construct a simple calculator, using modular structure. Create modules for each operation: add, subtract, multiply, divide, plus a module for pulling in all of those operations, just as you did in the diceroll exercise.
Build the math modules using TDD with Mocha and Chai assertions. Remember, with unit tests your concern is with individual functions that return some kind of value. Start with an empty module and a single test. Something like...
describe('add', () => {
it('should be a function', () => {
isFunction(add);
});
});It will fail, because this is the first code you have written for your app. There is no add method. Make that test pass by writing a function that does nothing, then rinse and repeat with every module until you have the skeleton of a project. Return to each method and write new tests for number of arguments, the type of data the function returns, whether the method returns anything at all, etc. Test multiple edge cases. What if no arguments are passed in? What if a string gets passed in where you need a number, or vice versa? What happens with negative numbers? Decimals? Leave no stone unturned!