Migrating our API tests from Postman to Jest


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At Seccl we’re using APIs to rebuild the infrastructure of investments and advice, and help forward-thinking advisers and disruptive fintechs to build the innovative investment platforms of the future.

Our APIs are used by a growing number of clients to power a fast-rising volume of investments and, unsurprisingly, we’re constantly developing and deploying new features.

While there are plenty of factors that can affect the pace and efficiency of our deployment cycles, automated testing is a big one. In fact, it’s absolutely key to us being able to release new changes at speed and with confidence.

Recently, we moved across 25 tests from a Postman/Newman infrastructure and, in the process, created around 100 tests in our new infrastructure. In this article I’ll explain why, how and what impact it’s had on our development process.

The way things were

We use Postman as a UI for interacting with our API and to create API docs. It allows you to store login tokens and other environmental variables – which is handy when working with multiple requests. It’s also great for manual testing and creating dummy data for things super quickly.

Until recently, we also created and managed our end-to-end tests inside a Postman collection, too. Although this gave us some automated testing coverage, it wasn’t the optimal approach, for several reasons.

Wait, Mr Postman…the problems we faced

PR for adding a new test with old stack (Postman)

PR for adding a new test with old stack (Postman)

Developing a solution

We had known for a while that we wanted to migrate to a better solution, and earlier this year we dedicated a six-week development cycle to migrate the tests over to a new framework.

Some of our QA team started by analysing and rewriting each of the Postman tests into BDD syntax, to spot where there were overlaps, understand where dependencies existed between the old tests, and create an easy way for us to write the new one and track our progress.

At the same time, several developers set about researching and experimenting with the underlying infrastructure and core machinery that the tests would sit on top of.

After that, we worked hard to rewrite the tests, with both developers and QA engineers writing code in the new framework.

The new stack

So what framework is that, exactly?

The benefits

This was a really worthwhile investment of time and we’re already seeing the benefits. In particular…

PR for adding a new test with new stack (Jest)

PR for adding a new test with new stack (Jest)

Some challenges

Inevitably there were some challenges along the way, the biggest one being testing asynchronous workflows.
By way of context, some parts of our API involve some asynchronous processing because of the way we use queues. For example, a test that creates a client, then an account, then sets up a payment, before confirming that payment and checking the payment has landed in the account…that doesn’t happen synchronously, so it’s not easy to work out of it has all been successful.
The solution was to create some reusable infrastructure for polling. We used the functional JS library ramda as really compact and neat way of creating rules to determine when the polling is done in a maintainable way.

Final thoughts?

It was a difficult process, but well worth the investment of time. We’re now adding new system tests alongside our development work at a much higher rate than before, and we spend much less time and energy dealing with failed tests.
All of which makes our process for deploying new and critical client functionality faster and more effective.