remove arrow function from mocha tests

removeArrowFunctionFromMochaTests.js

const _ = require('underscore');

const printOptions = {
    quote: 'single',
    trailingComma: true,
};

const mochaFunctions = [
    'describe',
    'it',
    'before',
    'after',
    'beforeEach',
    'afterEach',
    'context',
];

const isMochaLike = functionName => _.contains(mochaFunctions, functionName);

module.exports = function transform(file, api) {
    const source = file.source;
    const j = api.jscodeshift;
    const root = j(source);

    const isArrowFunction = n => n.type === j.ArrowFunctionExpression.toString();

    const filterMochaFunctionsCall = p => {
        const n = p.node;
        return n.callee.type === j.Identifier.toString() &&
            isMochaLike(n.callee.name);
    };

    root.find(j.CallExpression)
        .filter(filterMochaFunctionsCall)
        .map(p => {
            const args = p.get('arguments').value;
            const indexOfArrowFunction = _.findIndex(args, isArrowFunction);
            // if we didn't find an arrow function, exclude the result
            if (indexOfArrowFunction === -1) {
                return null;
            }
            return p.get('arguments').get(indexOfArrowFunction);
        })
        .replaceWith(p => {
            // replace with anonymous function expression
            // with same arguments list and same body
            return j.functionExpression(null, p.get('params').value, p.get('body').value);
        });

    return root.toSource(printOptions);
};