API Testing – Ultimate Guide for Beginners

APIs have been around since the 1960s, they are all around us. Every time you use rideshare app, do third party login, make payments and transactions, etc then you are using APIs. Without APIs the digital experiences that we expect everyday as consumers wouldn’t be possible. APIs are doing everything from driving information rich marketing campaigns to connecting mobile apps to streamlining internal operations. Here is a brief introduction to voice APIs and what they can do.

What is an API?

API is an acronym for Application Programming Interface that allows two different software programs to communicate with each other.API allows communication and integration between multiple applications to communicate with one another and share information.

You can think of API as a waiter, who takes your choices from the menu and brings them to the chef and delivers your finished meal.

Reasons for Developing API

– Functionality of software to be used by other software.

APIs provide a secure and systematized way for applications to work in conjunction. More precisely, API is a software to software interface. For instance, When you search for a flight on the “Make my trip” application,  flight details of different companies like Indigo, Vistara, Air India will appear.                                                                      

Are these companies owned by make my trip?

Definitely No, the functionalities of Indigo and others in the form of APIs are shared with make my trip to display flight details of these flight companies on its website.

This cannot be done without the help of API.

Let’s take a more familiar example to make you understand this concept.

You must be aware of Google authentication while logging in to other website when user doesn’t want to create separate account they can directly use Gmail address to login. In this process, Website is using API of Google.

– Reusing the application logic for creating different customized software.

Let say you have created an application already, now you want to create same application with a few advance features with some extra code. For that you don’t need to create application from scratch you can simply reuse the same application logic for creating next level up application. E.g.,

Visual studio application provides two subscription versions. One is community edition which is a free trial version while Other one is Professional edition which is a paid version in which along with community version features some extra will be provided. For this, developers will straightforwardly use API of community feature and for remaining addon features they will write the code.

– Reusing the application logic for different platforms.

When it comes to mobile application development, APIs play a vital role. APIs help web and mobile application connected to the important information that they deliver a great user experience.

Developers will create API for web application and that web application code will be reused in mobile application. They don’t need to code again for mobile application separately and within very less time mobile application will be developed by using APIs of the web app.

– Client Server Communication

When a client or a user browse any web page, request will be sent to the server and further we will get the response from that server. This whole communication between client and a server is happening through API requests travelling over the internet. To understand this communication in a more elaborative way, go through this example;

For login- you put valid email address and password. The moment you hit the login button from your laptop a request will be sent to the server and appropriate web service related to the login functionality will be triggered and simultaneously executed and your login credentials also being sent to the server over the internet. Server collects this email and password and processes it. As a part of processing this web service will do a SQL query on this database, a proper response will come back from database. That’s how communication ensued.

API versus Web services

Web services are available over the web that’s why the name came as web services. Basically, It exposes functionality of an application using APIs over web. Web services are a type of API.

Request and Responses are nothing but the APIs which are interacting with the web services and getting the things done. All web services are API ultimately but not all APIs are web services.

In APIs, communication happens directly not via internet. It has got integrate with the software itself. Two software don’t require internet to connect or send request and response.

For instance; “Workshare Professional” software which get integrated with the word document, excel etc. when installed. The moment you open your word document, you will get an extra option of “workshare” in the word itself. Here, workshare APIs are given to the MS word and they are interacting with each other.

Why to use APIs?

• It allows customer to access data server or any other applications in very stable and secured way in order to deliver high quality user experience.
• Mobile phones and devices embedded with sensors fit perfectly with the service based structure of APIs.
• APIs are mainly needed for both the initial migration and integration with other systems in the cloud.
• APIs offer flexibility that allows you to quickly leverage and use your desired services on mobile and web.
• The market is rising every subsequent year so certainly everyone wants their product or service to be the best which depends on how intuitive and usable their API is.
• The huge success of APIs has been the major reason to incorporate it in the development ecosystem. If any company has employed or deployed APIs and has been successful using that than other companies.

Why Test API?

If a customer facing public API breaks, entire chain of business processes would be at risk so testing the APIs is crucial.

• To make sure API does what it is supposed to do.
• To make sure API can handle the assigned load.
• To make sure API work across devices, browsers and systems
• To reduce business and automated test costs
• To detect all the way users can screw up the things

• Functionality: Ensure that the API functions as intended. Test that it returns the correct data, performs the expected actions, and handles errors appropriately

• Integration: APIs are often used to integrate different services or components of a system. API testing ensures that these integrations work smoothly and that data is exchanged correctly

• Reliability: Verify the reliability and stability of the API under various conditions, such as high loads, concurrent requests, and unexpected inputs

• Security : Identify and address potential security vulnerabilities, ensuring   that the API is protected against unauthorized access, data breaches, and other security threats

• Compatibility: Ensure that the API is compatible with various client applications, devices, and browsers

What is API Testing?

Testing the APIs to check whether the APIs that are developed resulting in proper responses with different possible inputs. To ensure the functionality and performance of APIs, API testing is performed.

APIs are often based on protocols and standard. It is performed at the most critical layer that is the business layer where business logic processing is carried out and all the transaction between the user interface and database happen.

API testing allows developers to start testing in the development cycle before their user interface is ready and kill bugs before they become serious problems which definitely saves time and money in a log run.API testing is critical because it guarantees connection between platforms.

Advantages of API Testing

• Improved test coverage: Testing APIs will give you more test coverage than UI testing. UI tests mainly focus  on the appearance and feel of the applications while API tests provide detailed and comprehensive coverage of  the functionality of the application.

• Earlier testing: We can test way before the UI is ready. In complex projects, after the development code is ready. Instead of waiting for UI which generally takes a few more days, software testers do not wait for UI to be ready rather they ask the developers to give the APIs and start testing APIs. And this early testing will help you get feedback sooner so that you can improve the team’s productivity.
• Faster release: API testing takes less time and reduce work load. Let say, you have an application which is on web, mobile, and desktop. Instead of testing the application separately on different platforms, you can only test on one platform if there it is working fine automatically the same application which is on different platform will also work fine because same API is being used in mobile UI, web UI and desktop UI.
• Language Independent: Data here is exchanged via JSON format so, any language can be used for automation independent of the language used in developing the application. JSON is typically structured data so the verification is literally very fast and stable. It also has built in libraries to support comparing data and different data formats.
• GUI independent: We can perform API testing within the application prior to GUI testing and this early testing will help you get feedback sooner so that you can improve the team’s productivity. Code functionality can be tested to expose minor errors and evaluate strength of your built application.

What kind of testing you can perform on API?

API testing can refer to various different types of tests depending on the objectives and circumstances.

• Mandatory fields testing

To ensure whether the API requests are working properly and giving an accurate response. Whenever you start testing APIs, generally you begin with checking mandatory and the most important fields despite scrutinizing all the fields in a single go.

• Functional testing

Functional testing ensures that the API functions working effectively and accurately. This test is performed to check correctness of functionality. It includes testing in the code base. Initially, happy paths will be checked followed by negative testing.

• Negative Testing

Negative Testing involves testing the APIs’ performance for possible wrong inputs. It focuses on finding potential bugs, coding errors and security weaknesses.

• Usability Testing

Ease of using APIs can be tested as a part of usability testing.  While using the APIs, you feel any complexity or difficulty in using it then usability would be a problem in this case which can be corrected once identified.

• Discovery testing

In discovery testing, we verify the documentations provided by the developers to software testers for testing the APIs. Basically, to test document verification whether the proper APIs and properties are provided for testing in the documents.

• Validation testing

After the completion of building the API, validation testing is done to make sure API is doing the same what it is supposed to do i.e., it validates the expected response or result. It involves checking input and output parameters and response format.

• Load or Stress Testing

Here, you are testing whether API can endure and handle the load that application might get. Will the code run with 1k requests, 10k requests or with 100k requests therefore, load testing tests API against regular traffic that API expects in ordinary usage.

• Security testing

Security testing ensures that the API implementation is secure from external threats and also aims to identify vulnerabilities in the API. It also involves validation of encrypted methodologies and access control for the API. Penetration testing is a part of security testing to stimulate attacks from hackers.

• UI and UX testing

UI testing is done to validate that the API works properly within User Interface of application. This type of testing is majorly used to check the UI end to end functionality.

• Reliability testing

To make sure that Response or output of the API is consistent, Reliability test is being performed. The output of API should be that what it is supposed to do. Primarily, here you will be checking if APIs can be consistently connected to whenever you want and lead to constant result always.

• Fuzz testing

In fuzz testing, testing will be performed by putting random or invalid data called fuzz into software system to detect coding errors, crashes and security loopholes. To perform fuzz testing, Automated and semi automated techniques are used.

• Unit testing

 Unit testing involves testing of a single function individually to ensure that each individual part is working efficiently. Mostly, the API testing is started by executing unit test first before performing integration testing.

• Interoperability testing

This type of testing implies to test SOAP APIs. Interoperability testing ensures the pre-define standards of your API has met. This majorly focuses on testing the communication and integration of different applications.

Use of tools in API testing

Google Chrome just show request and response but wouldn’t allow you to test. It is just a happy path scenario where you cannot modify any request URL or the input. Different variations we try in testing and this kind of testing is not possible with Google chrome. So, Chrome is not competent for testing APIs which required typical functionality tests. We need tools where we can test all possibilities where we can modify different things in the request URL, in body section, in pay load and many such things.

API Testing tools

There are several API testing tools available which we can use for performing the API testing not only in manual way but also we can automate the API testing.

• Postman                                                 
• ReadyAPI
• Fiddler
• Swagger
• JMeter
• Katalon studio
• TestGrid
• Subject7
• EggPlant
• SoapUI
• Tricentis Tosca
• UFT
• HTTPMaster
• vREST
• PingAPI
• Rest Assured
• Karate DSL
• Rest console
• Hippie-swagger
• Pyresttest
• Airborne
• APIPrayInspector
• SOAP Sonar
• Apigee
• Parasoft SOAtest

Conclusion

API testing is one of the most solid facets of maintaining an effective and successful API. If your API is bulky and not performing correctly then it certainly affects your application’s User interface and conclusively your users might jump to other reliable products. By understanding the fundamentals, mastering testing techniques, and utilizing effective tools, you can effectively test APIs and contribute to the overall success of your projects. As technology continues to evolve, staying updated with the latest trends and best practices in API testing will be essential for software professionals.