Feeds

A simple unit test for GUIs

Part 2: Server envy

Boost IT visibility and business value

Hands on Last time I described why GUI code is difficult to unit test, and why it's generally better to avoid doing so. But that doesn't mean GUI-related code shouldn't be tested - you just need to separate out the logic.

Easier said than done? The number of times I've spoken to Java GUI coders who've said: "Swing code can't be unit-tested, so we don't bother." Then they stare wistfully across the room at the server-side developers, whose code is well covered by tests.

So, how do you write unit tests for GUI applications? I'm not claiming that the approach described here is new, but it's simple, and I've found it to be highly effective as it promotes separation of concerns, putting the behaviour where the data is, and other good OO stuff.

First, let's assume you're creating a Swing-based Customer Details panel. So you'll want a CustomerDetailsPanel class that contains the GUI code: components, layout, and Swing event handlers. Next, create a Controller class, CustomerDetailsController, which will contain the business and application logic, and contain references to the entity objects (Beans, POJOs). Any time the GUI needs to check or update something related to the data, it makes a call to its Controller to do it.

The Panel and its Controller are tightly symbiotic: the Panel must know about the Controller in order to delegate to it, and the Controller must know about the Panel to tell it to update the GUI. Design puritans might start hyperventilating at this tightly coupled two-way relationship, but in practice it isn't a problem.

However, it could become a problem when you decide to write some unit tests for the Controller - which of course is the whole point of this exercise. If the Controller contains method calls to the Panel, then you'll also need to create an instance of the Panel in your unit test - something we're actively trying to avoid doing.

The easy solution is to define a UI interface (CustomerDetailsUI), implemented by the Panel and passed into the Controller on creation, which defines all the methods the Controller will want to call on the Panel. Then in your unit test, you can simply define a mostly-empty implementation of the UI interface and pass that into the Controller instance created for testing.

In the example I'm calling this a mock UI, although the Mock Object Correctness Police will doubtless rap my knuckles as it's really a stub implementation, not a mock.

Build a business case: developing custom apps

More from The Register

next story
KDE releases ice-cream coloured Plasma 5 just in time for summer
Melty but refreshing - popular rival to Mint's Cinnamon's still a work in progress
Leaked Windows Phone 8.1 Update specs tease details of Nokia's next mobes
New screen sizes, dual SIMs, voice over LTE, and more
PEAK LANDFILL: Why tablet gloom is good news for Windows users
Sinofsky's hybrid strategy looks dafter than ever
Fiendishly complex password app extension ships for iOS 8
Just slip it in, won't hurt a bit, 1Password makers urge devs
Mozilla keeps its Beard, hopes anti-gay marriage troubles are now over
Plenty on new CEO's todo list – starting with Firefox's slipping grasp
Apple: We'll unleash OS X Yosemite beta on the MASSES on 24 July
Starting today, regular fanbois will be guinea pigs, it tells Reg
Another day, another Firefox: Version 31 is upon us ALREADY
Web devs, Mozilla really wants you to like this one
prev story

Whitepapers

Implementing global e-invoicing with guaranteed legal certainty
Explaining the role local tax compliance plays in successful supply chain management and e-business and how leading global brands are addressing this.
Boost IT visibility and business value
How building a great service catalog relieves pressure points and demonstrates the value of IT service management.
Why and how to choose the right cloud vendor
The benefits of cloud-based storage in your processes. Eliminate onsite, disk-based backup and archiving in favor of cloud-based data protection.
The Essential Guide to IT Transformation
ServiceNow discusses three IT transformations that can help CIO's automate IT services to transform IT and the enterprise.
Maximize storage efficiency across the enterprise
The HP StoreOnce backup solution offers highly flexible, centrally managed, and highly efficient data protection for any enterprise.