API Testing Interview Questions

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Q. What API testing means?
API stands for Application Programming interface details regarding how some software components must act together. In general terms, API testing is a set of procedures and functions allowing the creation of apps accessing data or features of an operating system or application. All in all, testing of such procedures is acknowledged as API testing.
Q. What are the names of tests executed on APIs?
There can be numerous reasons behind executing API testing and there are a number of tests that can be performed on APIs. Some common API test examples are as follows:
1. Any data structure which demands proper validation can be updated by API
2. In case some interruption arises during the process or any other event is prompted, you can call to another API
3. Tests for inputting condition based return values can be performed
4. With the help of these tests some resources can be easily modified like process killing, update of the database, etc.
5. The return values can also be tested which can be even null or are with wrong results
Q. What is the procedure to perform API testing and what exactly needs to be checked?
During the API testing process, a request is raised to the API with the known data. This way you can analyse the validation response. Basically, things that must be checked during performing API testing are:
1. Accuracy of data 
2. Schema validation
3. HTTP status codes
4. Data type, validations, order and completeness 
5. Authorization checks 
6. Implementation of response timeout
7. Error codes in case API returns, and 
8. Non-functional testing like performance and security testing 
Q. What is the test environment of API?
To set up the test environment of API is not a cake walk. It is bit complete and demands the configuration of the database as well as server according to the need of the software. There is no availability of GUI (Graphical User Interface) in this form of testing.
Once the installation process is over, API is verified for the proper functioning. During the whole process API that is invoked by initial environment is being set up with distinct parameters to examine the test results.
Q. What approach should be followed for the API testing?
There are certain factors that determine the API testing approach. Let’s check them below:
1. Defining the accurate input parameters
2. Verifying the calls of the blend of two or more than two value added parameters 
3. Defining the basic functionality and scope of the API program
4. Writing suitable API test cases and making use of testing techniques like equivalence class, boundary value, etc. to verify the functionality 
5. Testing case execution 
6. Testing result comparisons with the results expected 
7. Verifying behaviour of API under conditions like the connection with files etc.
Q. Define the basic difference between API testing and UI level testing?
UI testing means the testing of graphical interface. It‘s focus is basically on the feel and look of an application. Within user interface testing, things like how user interacts with app elements such as images, fonts, layouts, etc is checked.
On the other hand API testing allows communicating between two different software systems. During this testing, a software system that implements an API includes sub-routines or functions that can be performed by other software system.
Q. Name the common protocols used in API testing.
Many protocols are there that can be used in API testing. These are as follows:
Q. Name different tools used for API testing.
There are many tools available that can be used for API testing. A few of them are:
Postman, SoapUi Pro, Curl, and Alertsite API monitoring 
Q. What is SOAP?
The term SOAP refers to Simple Object Access Control. In simple terms, it is an XML based protocol that helps in exchanging information among computers. 
Q. What’s the procedure to test API’s?
For testing API’s one must follows the below-mentioned steps:
1. Make a selection of the suite you like to add the API test case to
2. Now choose the test development mode
3. Next demands the development of test cases for the required API methods 
4. After this you need to configure the control parameters of the application and then test conditions
5. Once done with all the previous steps, configure method validation
6. Now is the time for execution of the API test
7. After this you can check test reports and filter API test cases 
8. Last but not the least, sequence all API test cases. That’s it!
Q. What is REST API?
REST API is a set of functions helping developers in performing requests along with receiving responses. Through HTTP protocol interaction is made in REST API. 
The term REST refers to Representational State Transfer. In very short span of time, it has become an effective standard for API creation.
Q. What are the areas that need to be taken care of while writing API document?
The main areas that need your concentration while writing API documents area as follows:
1. You need to check the source of the content 
2. Plan or sketch of your document
3. Delivery layout of the same
4. Information needed for each of the function available in the document
5. Lastly, automatic document creation programs
Q. What is API framework?
The API framework is easy to understand. During the process, config file is used to hold the configurable parts as well as to value the test run. Besides, within config file automated test cases hould be represented in the format of parse table. During the process of API testing, it is not mandatory to test each API as a result the config file contains some sections whose API is activated for all that specific run.
Q. What do you mean by input injection? Explain different ways of doing it.
The term Input injection is the act to stimulate user input. User input can be simulated in many different ways such as:
1. Direct Method Invocation 
2. Invocation with the help of accessibility interface
3. Doing simulation with the help of low-level input
4. Doing simulation with the help of a device driver 
5. Doing simulation with the help of a robot
Q. Define API testing with runscope.
To test APIs, Runscope is used. It is basically a web application providing backend services as well as an easy to use interface.
Q. Explain the major challenges come while API testing.
The list of major challenges that come while API testing are:
1. Parameter Combination
2. Parameter Selection and 
3. Call Sequencing 
Q. What are the main principles of API test design?
There are various principles of API test design. Those are as follows:
1. Setup: this includes the creation of objects, start services and initialize data, etc.
2. Execution: during this principle, there are steps to follow API or scenario as well as logging
3. Verification: for evaluating the execution outcome there is oracles 
4. Reporting: keep a tab on pass, blocked or failed
5. Clean up: this shows pre-test state 
Q. Explain the types of bugs that can be found using API testing?
API is capable of finding many types of bugs that includes:
1. Stress 
2. Security
3. Duplicate or missing functionality 
4. Reliability 
5. Unused flags
6. Performance 
7. Incompatible error handling 
8. Multi-threaded issues, and 
9. Improper errors 
Q. Name various tools used for API test automation.
While doing API testing and Unit testing, both targeting source code. In case an API method is making use of code based in .NET then other tool which is providing support must have .NET
There are various automation tools for API testing:
2. Soap UI
3. JUnit for Java
4. NUnit for .Net
Q. What is API documentation?
For any foundation, there is always a need of good documentation. Similarly API documentation provides as a quick reference to access working or library within a program.
While walking through any such documents, a proper plan is must along with proper sketch or layout for delivery, there is a need of content source, information regarding each and every function,etc.
There are various API documentation tools like Doxygen and JavaDoc. Below you can check the various categories in which each and every function is being documented that are revolving around the parameters like:
1. Function description
2. Type and syntax of error message that may occur
3. Syntax, elements and sequence needed for each parameter
4. Links regarding functions
Q. List some templates for API documentation that are most used.
There are various API documentation templates that are making the whole process really simple and easy. Check them below:
1. Swagger
2. Miredot
3. Slate
4. FlatDoc
5. API blueprint
6. RestDoc
7. Web service API specification
Q. Explain the difference between API testing and Unit Testing.
1. Where Unit testing is a form of white box testing, API testing is a form of black box testing. 
2. Unit testing is performed prior to the process of including the code in the build. On the other hand, API testing is done after the build is prepared for testing.
3. In the Unit testing, the source code is drawn in the form of testing while in API testing the source code is not drawn in.
4. In the Unit testing, there is the limited scope of testing as a result only basic functionalities are measured for the purpose of testing. Subsequently, in API testing there is wide scope of testing, thus all the issues that are functional are measured for the purpose of testing.
5. Unit testing is done by the testers and where in every functionality is separately tested. While The API testing is done by the testers for the purpose of end to end testing of the whole functionality.
Q. Define TestApi?
TestApi can be explained as the test building blocks library which is indispensable for testers and developers to create testing tools and automated test suites.
Q. Explain everything about warnings and API errors.
When something is not going as per expectations like when the outcome is not as predicted then the occurrence of errors can be seen and for the same warnings are explained in the form of a message in a proper format. Within a single module, there can be one or many warnings.
A wide range of warnings that can form are:
Missing module warning and parameter validation warning 
A wide range of errors that can form are:
1. Missing module errors
2. Documentation errors 
3. Parameter validation errors 
4. And some standard error messages
Q. Explain the working of API Builder.
API Builder is a PLSQL utility that includes 4 square files. To place API parameters and to begin the technique only one report is liable. API builder allows you to create and make use of API endpoints that can be guzzled by any client application.
There are several components that lead to the making of API Builder. During the working, files and formed for brief tables as well as master bundles for creating the output code. Lastly fourth record generates spooled output of the code into a record relating to as output_script_.sq.