when formatted with

Format a moment instance using any supported format, then delegate the formatted value to another assertion.

expect(moment('2015-11-02'), 'when formatted with', 'YYYYMMDD', 'to be', '20151102');

When the assertion fails you'll get this output:

expect(moment('2015-11-02'), 'when formatted with', 'YYYYMMDD', 'to be', '2015');

expected moment('2015-11-02T00:00:00.000+01:00')

when formatted with 'YYYYMMDD' to be '2015'

20151102

2015