Passes if the Date instance is between two other given instances:

var dateA = new Date(Date.UTC(2010, 10, 10));
var dateB = new Date(Date.UTC(2010, 10, 11));
var dateC = new Date(Date.UTC(2010, 10, 12));
expect(dateB, 'to be between', dateA, dateC);

To include the edge points as valid values you can use inclusively flag:

expect(new Date(0), 'to be inclusively between', new Date(0), new Date(1));

Failing assertions gives the following:

expect(
  new Date(Date.UTC(2010, 10, 10)),
  'to be between',
  new Date(Date.UTC(2010, 10, 10, 0, 0, 1)),
  new Date(Date.UTC(2010, 10, 10, 0, 0, 2))
);

expected new Date('2010-11-10T00:00:00Z')
to be between new Date('2010-11-10T00:00:01Z') and new Date('2010-11-10T00:00:02Z')