API Testing Interview Questions and Answers

API stands for Application Programming Interface which acts as an interface between two applications and allows them to communicate with each other. In simple words, APIs ensure how one part of the software program interacts with the other part and allow exchanging of data between systems that are located at different remote places.

Working of APIs

Let’s understand this with the help of a simple flow diagram-

In API Testing, responses based on the following parameters will get analyzed.

• Testers or developers have to analyze the data accuracy which they have received by comparing it with the expected response.
• Time is taken by the API to respond.
• Error codes need to be analyzed if APIs are expected to throw an error.
• HTTP status codes.
• Non-functional specifications like the security, performance, availability, etc. of an application need to be tested.
• Authorization checks

Term REST refers to Representational State Transfer which is a set of functions and thus helps developers in making requests along with receiving responses. In Rest API interaction is made with HTTP protocol and in a very short time, it becomes a productive standard for API creation.

Like another software testing, API testing also faces some challenges described below-

• To know about the proper input values that need to be entered in API inputs because of the absence of GUI.
• One must have proper knowledge of output verification and validation.
• Challenge of proper parameter selection and its combination.
• Strong coding knowledge is a must for testers too.

UI means User Interface is a type of testing that generally tests the graphical interface means to test how an application is looking, how it is feasible for end-users, Images, buttons, videos, font displayed on UI screen are working as expected.
While API means the program interface that permits communication between two different programs. Its main focus is on the business layer of an application.

When you see the word automation, it means to ease human work with the help of software and tools. 

• In the coming years, automation testing will cover 80% of the test coverage of any application in a shorter time means automated testing helps to test large and many test cases very easily and quickly.
• It allows parallel execution and helps in reducing the number of errors that could be generated by humans.
• It saves the time required to test the applications manually and thus saves the overall cost of any project.
• Testers don’t have to worry about the part of the application that requires retesting.
• Helps in identifying defects or bugs at an early phase of development without having any access to the User interface.

For smooth working and seamless working experience it is advisable to follow some practices that make API Testing more successful-

• Don’t Repeat Yourself: Avoid repeating the code, in case some tests need the same components and actions it’s better to create a common library.
• Clarity: Write test cases clearly so that they can be easily debugged. Clear test cases which are running successfully hardly require any attention or time.
• Mapping and Execution: Design the test in such a way that it can execute in any working environment
• Utilization of complete API Testing Tool: An all-inclusive API testing tool by your side is very important as it provides features like creating multi-step testing scenarios, effortless testing, tracking API performance, and automated API documentation, etc.
• Monitor Security Checks: It is a must to design API security test cases for any security breach or flaws.
• Tackle Negative Testing: Apart from monitoring positive responses one should also opt for negative test results as this process helps in mapping the performance while dealing with issues.

• Weather Reports: Weather reports can be found on all platforms like Google Search, Apple’s weather app, or from any Smart device. Now, these platforms are not in the business of weather data, so they take this source of information from a third party and do it with the help of API.
• Log-in Using Facebook/Twitter/Google: You ever saw this sentence “Login to your account” - Every time any application loads, it checks with the help of API if a user is already logged by any of these media, if not API provides identification information.
• Pay with PayPal: Ever pay using PayPal in any eCommerce store? Well, that also uses API to work and is very similar to the login process.
• Twitter Bots: All bots means the account that automatically tweets, follows, sends messages are handled by Twitter API.
• Travel Booking: Ever thought about how travel booking sites can show thousands of flights and destinations with the cheapest option? This is because of using third-party APIs to collect flight information from providers.

API Testing is considered the most suitable form of Automation Testing because of the following reasons.

• API testing provides the most stable interface and hence allows two programs to communicate with each other.
• It provides faster feedback as API acts as an interface between the user and the application. 
• It successfully validates all the functional paths of the system which are under test.
• In API testing testers can run API tests without any access to the user interface of software applications.
• API Testing is language independent and hence users can select any core language when executing automation tests for the application.

We have already discussed API Testing in detail, how it provides accuracy in an application and hence capable of finding many types of bugs that includes-

• Poor Performance
• Fail to handle requests in a secured manner
• Duplicate or missing API functionality due to the repetition of code
• Fail to handle negative test cases
• If there is heavy traffic or stress, then it is failed to handle that sudden spike.
• Issues in Multi-threading
• Improper error codes and status codes
• Reliability of the software
• Throw error at unused flags
• Incompatible error handling process
• Improper messaging