How to capture and return value?

I’m trying to do both a capture and return on the same mock, but I can’t figure out how to set it up. This is my attempt so far:

const mockedDS = mock(MyDataService);
const whenCall = when(mockedDS.update(anything(), anything());
whenCall.thenReturn("OK");
const firstCaptor = new Captor<Array<Employee>>();
const secondCaptor = new Captor<TimePeriod>();
whenCall.thenCapture(firstCaptor, secondCaptor);

It seems that I can only do one or the other? Depending on whether I call thenCapture before thenReturn or vice versa it will only capture OR return the value.

Btw. What I’d really like to write is this;

const mockedDS = mock(MyDataService);
const firstCaptor = new Captor<Array<Employee>>();
const secondCaptor = new Captor<TimePeriod>();
when(mockedDS.update(anything(), anything())
    .thenCapture(firstCaptor, secondCaptor);
    .thenReturn("OK");

…but both thenReturn and thenCapture returns void