a simple shim for ava's it.failing function

failing.js

function failing (ctx, name, fn) {
  const error = () => { throw new Error('remove the failing bit') };
  if (fn.length > 0) {
    return ctx(name, function (done) {
      fn(function(err) {
        if (!err) {
          return done(error());
        }

        return done();
      });
    });
  }

  return ctx(name, function () {
    try {
      const retVal = fn();
      if (retVal && typeof retVal.then === 'function') {
        return retVal.then(() => Promise.reject(error()), () => Promise.resolve());
      }
    } catch (e) {
      return;
    }

    error();
  });
}

describe('outer', function () {
  failing(it, "promise fail", function () {
    return Promise.reject();
  });

  failing(it, "promise succeed", function () {
    return Promise.resolve();
  });

  failing(it, "callback fail", function (done) {
    done(new Error());
  });

  failing(it, "callback succeed", function (done) {
    done();
  });

  failing(it, "sync fail", function () {
    throw new Error();
  });

  failing(it, "sync succeed", function () {

  });
});