[Part 01] API Testing Basics: SOAP API & REST API
In this article, we will learn about API Testing Basics, exploring SOAP API & REST API. This will be a series. So, please read the other parts to learn more about this.
Application Programming Interface (API)
What is an API?
Application Programming Interface, or API, defines how a component should communicate with another. It comprises several methods, conventions, and creation tools for software applications.
What is a web service?
A Web service is an open set of standards and protocols frequently used to transfer data between applications or systems.
Differences between Web Services and API
| Web Service | API |
| All web services are APIs. | All APIs are not web services. |
| It supports XML. | Responses are formatted using Web API’s Media Type Formatter into XML, JSON, or any other format. |
| You need a SOAP protocol to send or receive data over the network. Therefore, it does not have a lightweight architecture. | API has a lightweight architecture. |
| It can be used by any client who understands XML. | It can be used by a client who understands JSON or XML. |
| Web service uses three styles: REST, SOAP, and XML-RPC for communication. | Any type of communication can use API. |
| It provides support only for the HTTP protocol. | It supports the HTTP/s protocol: URL Request/Response Headers, etc. |
How does API work?
An application programming interface, or API, functions as a messenger, receiving requests from a portion of a system, sending them to another, and then returning the answer.
Imagine you’re ordering food at a restaurant. You tell the waiter what you want (the request) to order, the waiter takes your order to the kitchen (where the work is done), and then the waiter brings your food back to you (the response). The waiter in this example is like the API. The API helps different software programs communicate by taking requests, sending them where they need to go, and returning the results.
API Structure
What is Middleware?
Software that serves as a connection between several systems and applications is known as middleware. It allows them to communicate and exchange data seamlessly, even running on different platforms or using various programming languages.
Suppose you have a website where visitors can register. Before providing access to specific pages, middleware may verify whether the user is logged in. The middleware would send users to the login page if they weren’t logged in. It functions similarly to a checkpoint, ensuring everything is in order before proceeding.
Why is API testing necessary?
API Testing ensures the Application Programming Interface performs what it is supposed to.
- Make sure that the application programming interface can manage the load.
- To ensure that the Application Programming Interfaces work across browsers, devices, and OSs.
- With the Application Programming Interface test, expenses could be involved because of system failure.
Types of API Testing
Some commonly used APIs are:
SOAP API
What is SOAP API?
- A protocol for exchanging structured information in a decentralised, distributed environment.
- Uses XML to define messages and WSDL (Web Services Description Language) to describe web services
- SOAP API is well-suited for enterprise applications that require high security and reliability.
Workflow of SOAP API Testing
- A client application sends a SOAP API request to a SOAP API server.
- The following information is contained in the XML document that represents the SOAP request:
- The name of the operation to be performed
- The parameters of the operation
- The SOAP API server processes the request and sends a SOAP response back to the client application.
- The SOAP API response is an XML document that contains the following information:
- The result of the operation
- Any error messages
Benefits of SOAP:
- Security: SOAP API supports multiple security standards, such as SSL and WS-Security.
- Reliability: It is a mature technology that has been widely adopted.
- Standardisation: It is a standardized protocol that makes integration with other applications accessible.
Drawbacks of SOAP:
- Complexity: SOAP API is a complex protocol that can be difficult to learn and implement.
- Verbosity: Its messages are verbose and can be large, impacting performance.
- Rigidity: It is a rigid protocol that allows for little flexibility in how applications interact.
REST API
What is REST API?
A REST API enables various software systems to interact with one another via the Internet. It enables using standard web techniques to send requests from one system to another and receive replies.
How does REST API work?
- A client application sends an HTTP request to a REST server.
- The HTTP request specifies the following information:\
- The HTTP method (GET, POST, PUT, DELETE)
- The URI of the resource
- After processing the request, the client application receives an HTTP response from the REST server.
- The HTTP response specifies the following information:
- The HTTP status code (200 for success, 404 for not found, etc.)
- The response headers
- The response body, which is the representation of the resource
Benefits of REST API:
- Simplicity: REST API is a simple and easy-to-understand architectural style.
- Flexibility: It’s a flexible style that can be adapted to various applications.
- Performance: It’s a lightweight style that can be very performant.
- Scalability: It’s a scalable style that is easily deployed to distributed systems.
Drawbacks of REST API:
- Lack of standardisation: REST API is not a standardised style, making it difficult to integrate with other applications.
- Security: Although unique security systems are needed, REST lacks built-in security capabilities.
- Statefulness: REST API is a stateless style, making it difficult to track the state of a conversation between a client and server.
Difference between SOAP and REST API
| SOAP | REST |
| 1. Standardized protocol with predefined rules | 1. Architectural design with fewer guidelines |
| 2. function driven(data as service) | 2. Rest is data-driven(data as a resource) |
| 3. Stateful or stateless | 3. Stateless |
| 4. No Caching | 4. Caching supported |
| 5. WS security & SSL | 5. HTTP and SSL |
| 6. Very secure | 6. Less secure |
| 7. Require more bandwidth and computing power | 7. Require fewer resources |
| 8. Supports only XML file | 8. Support different types of files (XML, HTML, JSON, YAML, etc) |
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