Mocha snapshot test

mocha-snapshot-test.js

const { writeFileSync } = require('fs');
const prettyFormat = require('pretty-format');
const reactTestPlugin = require('pretty-format/plugins/ReactTestComponent');
const reactElementPlugin = require('pretty-format/plugins/ReactElement');

let globalForceUpdate = false;
if (process.argv.includes('--snapshots-update')) {
    globalForceUpdate = true;
}

const serialize = (key, content) => {
    const escapedContent = content.replace(/\\/g, '\\\\')
                                  .replace(/`/g, '\\`')
                                  .replace(/\$/g, '\\$')
                                  .replace(/^\n|\n$/g, '');
    return `exports[\`${key}\`] = \`\n${escapedContent}\n\`;\n`;
};

const serializeFile = fileContents => {
    const linterDisable = '/* eslint-disable */';
    const contents = Object.keys(fileContents).map(key => {
        return serialize(key, fileContents[key]);
    }).join('\n');

    return `${linterDisable}\n${contents}`;
};

const deserialize = content => {
    return content.replace(/^\n|\n$/g, '');
};

const toMatchSnapshot = ({ fileName, name, forceUpdate = false }, content) => {
    if (!fileName) {
        throw new Error('toMatchSnapshot: fileName is required');
    }

    if (!name) {
        throw new Error('toMatchSnapshot: name is required');
    }

    if (!content) {
        throw new Error('toMatchSnapshot: content is required');
    }

    const prettyContent = prettyFormat(content, {
        plugins: [reactTestPlugin, reactElementPlugin]
    });

    let sourceContent;
    let toBeSaved;

    // try to load the file
    try {
        const jsonSnapshotSource = require(fileName);
        if (!jsonSnapshotSource[name] || forceUpdate || globalForceUpdate) {
            sourceContent = jsonSnapshotSource[name] = prettyContent;
            toBeSaved = serializeFile(jsonSnapshotSource);
        } else {
            sourceContent = jsonSnapshotSource[name];
        }
    } catch (e) {
        toBeSaved = serializeFile({
            [name]: prettyContent
        });
        sourceContent = prettyContent;
    }

    // save in JSON format
    if (toBeSaved) {
        writeFileSync(fileName, toBeSaved);
    }

    const message = `Received content doesn't match the snapshot in ${fileName.replace(process.cwd(), '')}`;
    assert.equal(deserialize(sourceContent), prettyContent, message);
};

module.exports = toMatchSnapshot;