What is API or Application Program Interface?

Application Program Interface or API is a method for many applications to interact with each other with the help of a common language which is often defined by a contract. Like the UI lets a human communicate with an application, APIs let the machines to interact with each other efficiently. APIs are great as they represent the building blocks that the developers can easily use to assemble all kinds of interactions without writing an interface every time they require machines to interact. Also, as APIs have the contracts, apps that are wanting to interact with each other can be created in different ways until and unless they interact according to the API contract. This lets many developers from many countries in many parts of the world to build highly distributed applications while reusing the same APIs.

When a user is interaction with the front end of an app, that front end forces the API to make calls to the backend systems which simplifies the development process in two ways.

1. The developer must have no concerns about making a customized app for every mobile device or browser.
2. Different backend systems are updated or modified without redeploying the complete application every time. This will help in saving time to accomplish a different task rather than writing the logic into the application.

What does API test entail? How to do it?

Unlike the user who is interacting with the app at the UI level, the developer must make sure the reliability of any underlying APIs. Without testing the APIs, developers would be stuck in manual testing just like a user, testing the app at the UI level. Rather than this, you can perform automated API testing by testing the app at the API level, designing test cases that directly interact with the underlying APIs, and achieving many benefits including the ability to test the business logic at a layer that makes it easy to automate in a stable way.

The best way to implement API testing is by building a solid testing practice from the bottom up. This way, you can design a test strategy by following Martin Fowler’s testing pyramid. The approach suggests that you build an array of API test on a foundation of unit tests with the UI tests on a Continuous Testing Platform. The tests let you to test application logic at a level where the unit tests cannot. These strategies are complementary.