Developers that work on front-ends have it easy . When it comes to doing a sprint demo or showcasing your work you’ve got something glitzy to talk about. In contrast writing a service API is remarkably dull by comparison.
At the bottom end of the spectrum you have got good old reliable CURL, if you want a command-line feel to your demo. Just above this, but also still fairly dry by comparison with a proper UI, is using a GUI based HTTP tool such as the Postman or Advanced REST Client extensions for Chrome. Either way it’s still pretty raw. Even using tools like Swagger still put you in the mind-set of the API developer rather than the consumer.
If you’re writing a RESTful API then it’s not much effort to write a simple front-end that can invoke your API. But there’s more to it than just demoing which “feature” of an API you delivered, it has other value too.
One of the hardest things I’ve certainly found working on service APIs is how you elevate yourself from being the implementer to being the consumer. Often the service I’m working on is one piece of a bigger puzzle and the front-end either doesn’t exist (yet) or is being developed by another team elsewhere so collaboration is sparse.
When you begin creating an API you often start by fleshing out a few basic resource types and then begin working out how the various “methods” work together. To do this you need to start thinking about how the consumer of the API is likely to interact with it. And to do that you need to know what that higher level use cases are (i.e. the bigger picture).
This process also leads directly into the prioritisation of what order the API should be built. For instance it’s often assumed the Minimum Viable Product (MVP) is “the entire API” and therefore order doesn’t matter, but it matters a lot as you’ll want to build stuff your consumers can plug-in as soon as it’s ready (even just for development purposes). Other details may not be fleshed out and so you probably want to avoid doing any part of it which is “woolly”, unless it’s been prioritised specifically to help drive out the real requirements or reduce technical risk.
A simple UI helps to elevate the discussion so that you don’t get bogged down in the protocol but start thinking about what the goals are that the customer wants to achieve. Once you have enough of a journey you can start to actually play out scenarios using your rough-and-ready UI tool instead of just using a whiteboard or plugging in CURL commands at the prompt. This adds something really tangible to the conversation as you begin to empathise with the client, rather than being stuck as a developer.
This idea of consuming of your own product to help you understand the customers point of view is known as “eating your own dog food”, or more simply “dog-fooding”. This is much easier when you’re developing an actual front-end product rather than a service API, but the demo UI certainly helps you get closer to them.
I’ll be honest, I love writing tools. If you’ve read “From Test Harness To Support Tool” you’ll know that I find writing little tools that consume the code I’ve written in ways other than what the automated tests or end user needs is quite rewarding. These usually take the form of test tools (commonly system testing tools ), and as that post suggests they can take on a life later as a support or diagnostic tool.
Given that the remit of the demo site is to drive the API, it can therefore also play the role of a testing tool. Once you start having to carry over data from one request to the next, e.g. security token, cookie, user ID, etc. it gets tedious copying and pasting them from one request to the next. It’s not uncommon to see wiki pages written by developers that describe how you can do this manually by copy-and-pasting various steps. But this process is naturally rather error prone and so the demo site brings a little automation to the proceedings. Consequently you are elevated from the more tedious aspects of poking the system to focus on the behaviour.
This also gels quite nicely with another more recent post “Man Cannot Live by Unit Testing Alone” as I have used this technique to find some not-insignificant gaps in the API code, such as trivial concurrency issues. Whilst they would probably have been found later when the API was driven harder, I like to do just a little bit of poking around in the background to make sure that we’ve got the major angles covered early on when the newer code is fresher in your mind.
This can mean adding things to your mocks that you might feel is somewhat excessive, such as ensuring any in-memory test data stores (i.e. dictionaries) are thread-safe . But it’s a little touch that makes exploratory testing easier and more fruitful as you don’t get blasé and just ignore bugs because you believe the mocks used by the API are overly simple. If you’re going to use a bit of exploratory testing to try and sniff out any smells it helps if the place doesn’t whiff to begin with.
3rd Party Test UI
One of the problems of being just one of many teams in the corporate machine is that you have neighbours which you need to play nicely with. In the good old days everyone just waited until “the UAT phase” to discover that nothing integrated correctly. Nowadays we want to be collaborating and integrating as soon as possible.
If I’m building an API then I want to get it out there in the hands of the consumers as soon as possible so that we can bottom out any integration issues. And this isn’t just about fixing minor issues in the contract, but they should have input into what shape it should take. If the consumers can’t easily consume it, say for technical reasons, then we’ve failed. It’s too easy to get bogged down in a puritanical debate about “how RESTful” an API is instead of just iterating quickly over any problems and reaching a style that everyone can agree on.
The consumers of the service naturally need the actual API they are going to code against, but having access to a test UI can be useful for them too. For example it can give them the power to play and explore the API at a high-level as well, potentially in ways you never anticipated. If the service is backed by some kind of persistent data store the test UI can often provide a bit of extra functionality that avoids them having to get your team involved. For example if your service sends them events by a queue, mocking and canned data will only get them so far. They probably want you to start pushing real events from your side so that they can see where any impedance mismatches lie. If they can do this themselves it decouples their testing from the API developers a little more.
When you’re building a utility service at a large company, such as something around notifications, you might find that the product owner needs to go and talk to various other teams to help showcase what you’re building. Whilst they are probably already in the loop somewhere having something tangible to show makes promoting it internally much easier. Ideally they would be able to give some immediate feedback too about whether the service is heading in a direction that will be useful to them.
There is also an element of selling to the upper echelons of management and here a showcase speaks volumes just as much as it does to other teams. It might seem obvious but you’d be amazed at how many teams struggle to easily demonstrate “working software” in a business-oriented manner.
How Simple Should It Be?
If you’re going to build a demo UI for your service API you want to keep it simple. There is almost certainly less value in it than the tests so you shouldn’t spend too long making it. However once you’ve got a basic demo UI up you should find that maintaining it with each story will be minimal effort.
 Yes, I’m being ironic, not moronic.
 I’ve worked on quite a few decent sized monolithic systems where finding out that’s going on under the hood can be pretty difficult.
 Remember your locking can be as coarse as you like because performance is not an issue and the goal is to avoid wasting time investigating bugs due to poorly implemented mocks.