Using Divvy for rapid testing of Responsive Design
An interesting approach to quick testing of your responsive designs against the viewport by setting up a series of keyboard shortcut widths using Divvy.
Whilst there is no substitute for testing on actual devices and we should exercise caution at designing for predetermined breakpoints, I’ve found having a quick way of checking a design at different viewports on my Mac has massively helped me working on responsive website designs.
An excerpt from Using Divvy for rapid testing of Responsive Design