How to use the mock-fs function in mock-fs

beforeEach(async function mockValidProjectLayout(done) {
            mockFs({
                'path/to/testsuites': {
                    'sakuli.properties': `
                        sakuli.environment.similarity.default=0.99
                    `,
                    'suite': {
                        'testsuite.properties': `testsuite.name=test`,
                        'testsuite.suite': stripIndent`
                            case1/sakuli_demo.js http://sahi.example.com/_s_/dyn/Driver_initialized
                            case2/sakuli_demo.js http://sahi.example.com/_s_/dyn/Driver_initialized
                        `,
                        case1: {
                            'sakuli_demo.js': '// Test'
                        },
                        case2: {
                            'sakuli_demo.js': '// Test'
                        }

export function initWithoutTree(){
    mock(filesWithoutTree);
}

export function initEmpty(){
    mock(filesEmpty);
}

export function initWithErrorTree() {
    mock(filesWithErrorTree);
}

function mockFs() {
  mock({
    [testDir]: {
      [showFolder]: mock.directory({
        birthtime: pastDate,
        items: {
          [showFile1]: f(pastDate),
          [showFile2]: f(pastDate),
          [showFile3]: f(pastDate),
          [showFile4]: f(pastDate)
        }
      }),
      [movieFolder]: mock.directory({
        birthtime: nearestDate,
        items: {
          [movieFile]: f(nearestDate)
        }
      })

export function initWithTree(){
    mock(filesWithTree);
}

export function mockFsWithCwd(config, cwd) {
  mockFs(config, {
    createCwd: false
  });
  process.chdir(cwd);
}

beforeEach(done => {
      mockFS(mockFileSystem);
      done();
    });

export function initWithoutTree(){
    mock(filesWithoutTree);
}

before(function() {
        mockfs(mockTree);
        this.spawn = childProcess.spawn;
    });