ForEach Testing Example

attempt-failing.js

console.log(0);
console.log(1);
console.log(2);
console.log(3);
console.log(4);
console.log(5);
console.log(6);
console.log(7);
console.log(8);
console.log(9);

attempt-passing.js

for(var i=0;i<10;i++){
    console.log(i);
}

solution-tester.js

const path = require('path');

console = {
    log: jest.fn()
};
const theFile = '../for-loop.js';

describe('for loop and console log output', () => {
    require(theFile);

    it('should call the console log 10 times', () => {
        expect(console.log.mock.calls.length).toBe(10);
    });

    it('should call log all 10 numbers', () => {
        for(var i=0;i<10;++i){
            expect(console.log.mock.calls[i][0]).toBe(i);
        }
    });

    it('should not cheat', () => {
        var fs = require('fs');

        function countInstances(string, word) {
            var substrings = string.split(word);
            return substrings.length - 1;
        }

        const pathToFile = path.join(__dirname, theFile);
        const text = fs.readFileSync(pathToFile, 'utf8');
        const instances = countInstances(text, 'console.log');
        expect(instances).toBe(1);
    });
});