Mocking chained APIs with Jest, the easy way

mock-chained-api.ts

// for when you want to mock/stub chained APIs
// useful with stuff like octokit, aws-sdk, neo4j-driver
// for avoiding nastiness, like, for e.g. octokit.git.getTree
// const octoStub = { octokit: { git: { getTree: jest.fn()) } } }

// this mocks/stubs everything to a specified depth
function mockChainedAPI(mock: any = jest.fn(), depth: number) {
  return new Proxy({} as any, {
    get: function(obj, prop) {
      obj._depthCount = (obj._depthCount || 0) + 1;
      if (obj._depthCount === depth) {
        return mock;
      }
      obj[prop] = function() {
        return this;
      };
      return obj[prop];
    }
  });
}