Prettier 1.15.1
Playground link

--parser babylon

Input:

  it(
    'succeeds if the test finishes in time',
    () => new Promise(resolve => setTimeout(resolve, 10)),
    250
  );

Output:

it("succeeds if the test finishes in time", () =>
  new Promise(resolve => setTimeout(resolve, 10)), 250);

Expected behavior:
Not sure, actually. But I find it pretty hard to read at first glance that 250 is an argument to it and not part of the statement in the body of the callback function.

Related to #5085 (FWIW, I'm highly supportive of that change, I just think the arrow return case is hard to read)