Jest + Filesystem mocks

files.js

//your files

module.exports = {
    "src/a.js": `const b = require("./b");module.exports = class A {}`,
    "src/b.js": "module.exports = class B {}",
};

fs.js

//__mocks__/fs.js
module.exports = require("memfs");

fs.spec.js

jest.mock("fs"); // we need this if some of your code uses "fs", so we make sure they use the mocked variant
const { fs, vol } = require("memfs");

const fixtures = require("./fixtures/files");

describe("fs", () => {
    beforeEach(() => {
        vol.fromJSON(fixtures, `${__dirname}/fixtures`);
    });

    afterEach(() => {
        vol.reset();
    });

    it("can operate on virtual in memory files", () => {
        expect(fs.existsSync(`${__dirname}/fixtures/src/a.js`).toBeTruthy();
    });
});