API Testing vs Web Services Testing

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When we talk about APIs and Web Services, while being related to each other to some extent, there are a lot of aspects which can help you to differentiate between them. Thus the API testing and web service testing have some differences which we are going to discuss in this article.

First, let’s get to the basics and discuss what they actually mean. An API or Application Programming Interface is a set of data structures, object classes, protocols and routines provided by the libraries and/or operating system services, which support the building of an application. On the other hand, a web service is a software system that is aimed to support the communication between two machines within a network.

By just looking at the definitions of these two it can be stated that both of them are means of communications. However, the web services include communication over the network almost all the time and HTTP is the most common protocol web services use. It also uses SOAP, REST and CMP-RPC as modes of interaction between two machines. On the other hand, API is a mode of communication regardless inclusion of a network. It can communicate via DLL files in C/C, Interrupts in Linux Kernel APIs and Jar files in Java and so on.

The Testing Structure of API and Web Services

Each and every mode of communication needs to be tested before it is made available for the general public. Any web services or APIs that are available in the public domain has to go through vigorous testing to ensure there are no loopholes, which hackers and spammers can use to harm the software, or those who are using the software.

The API testing approach:

  • First of all, it is important to understand the functionality of the API program. The scope of the program has to be defined on the first step to making sure the testing can be done keeping the perspective usage of the program.
  • Different testing techniques that involve boundary value analysis, equivalence classes and error guessing are involved in the testing process. The team also needs to write test cases for the APIs.
  • Each and every input parameter of the API has to be planned and defined in the proper format to make it easy to track any loophole.
  • Once every data on the hypothetical side is ready, tests cases are executed on API and the predicted results and actual results are compared to see if the API is working properly or not.

In order to make sure everything is running smoothly, the following testing methods should be included along with the usual SDLC process.

  • Discovery Testing: Every set of calls should be executed manually that are documented in the API. For example, the test group should check if a specific resource that is being exposed by the API while running the application can be listed, created and deleted when required to avoid any unwanted exposure.
  • Usability testing: the test group needs to verify that the API is fully functional and user-friendly. Also, it is important to test if the API runs smoothly of different platforms.
  • Security testing: This testing phase determines if the API uses authentication or not. If not, the test group will mark it insecure and if it requires authentication then the security level of the authentication is used. Also, it is checked if the sensitive data that is being transferred from one location to another is encrypted over HTTP or not. It is important to make sure that all the private information is properly encrypted to avoid any leakage during the data transfer.
  • Test Automation: The API is tested for its scripts and tools that can be used to execute the application regularly.
  • Documentation: The documentation included as the result of the testing should be detailed and well explained at each step. It is important to provide the documentation of testing with the API.

Web service testing approach

  • You can call web services by a software application by using HTTP protocol or SOAP.
  • There are many ways to implement Web Services but the most common approaches are SOAP (Simple Object Access Protocol) and REST (Representational State Transfer architecture).
  • The software applications interact with each other and share data using the web services.
  • SOAP is based on data exchange via XML while REST is based on data exchange via CML, Json and simple URL.
  • There is an XML based language known as WSDL, which is used to define services offered by web services like SOAP.

In order to test web services, you can opt to create your own code. For example, you can use Axis2 API for Java can be used. However, with the help of automation tools like SoapUI you can reduce your coding efforts.

When it comes to web service testing, there are few points involved such as:

  • Understanding the WSDL file and its functionality.
  • Determining the operations that the web service under the testing phase can provide.
  • Determining the request formats based on XML which need to be sent for the communication and data transfer.
  • Determining the response that is received in the XML format.
  • Usage of a tool or a specially designed code to send and receive requests and responses and validate them properly.
  • Documentation of the testing is required to understand if everything is working smoothly without any loopholes.

Let’s take an example here. Imagine you want to test a tool that provides currency conversion in real time. The service that the application uses should be able to convert the values of one currency to another using the rates provided by the international entities via different codes available for these specific purposes.

Conclusion

When it comes to APIs and Web Services, both the aspects of the data transfer mechanism require vigorous testing based on the protocols defined to ensure that they are safe for the use on and off the network. The applications based on APIs and Web Services should be safe and secure to avoid any hacking attempt. The testing of APIs and Web Services include different steps and have some differences which the test team needs to keep in mind while performing tests and providing the results.

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