What is Eval in Karate Framework?

Karate framework is an open-source automation testing tool used for testing web services, API, and micro-services. It is an easy-to-learn tool with minimum Java programming knowledge required to write test scripts. Eval is one of the vital features provided by the Karate framework. In this blog post, we will go through what is eval in Karate framework.

Eval in Karate Framework

Eval is an essential feature of Karate which is used to execute JavaScript code. It is one of the most powerful features Karate has to offer. Testers use eval to modify payloads, headers, or to execute some logic dynamically. It is a built-in feature that allows the user to execute JavaScript code during test execution.

Eval wants JSON in its response. Karate converts other formattings into JSON before passing it to the eval method. The Eval method takes a string argument that needs to be executed where the JSON object will be returned as the result.

Example Usage of eval –

„`
* def profile = {firstName: ‚John‘, lastName: ‚Doe‘}
* def first = eval(‚profile.firstName‘)
* print first
„`

In the above example, we have saved a JSON object in profile. Using an eval statement, we have extracted the firstName value from the profile object and saved it to another variable named first. At the end of the script, the first value will be printed.

Why to use Eval?

Karate is a powerful API testing tool, and by using eval, we can further enhance the capabilities of Karate. Some of the essential use cases of eval are as follows,

• Dynamic Payloads – Eval can be used to modify the payload dynamically based on the test scenario.
• Header Modification – Eval can be used to modify headers dynamically based on the test case.
• Custom logic execution – Eval can be used to execute custom business logic during the test run.

Eval limitations and best practices

Eval is a powerful feature of the Karate framework, but there are some limitations and best practices that need to be followed.

• Eval should only be used when it is necessary. As eval is a JavaScript code execution feature, doing too much with it can lead to performance issues.
• Eval execution can have dependencies on external JavaScript modules. Make sure to add them to the Karate config file.
• While using eval, make sure to adhere to JavaScript syntax.

What is Eval in Karate Framework?

Karate is a popular open-source framework that is being used widely for automated testing of web services. Eval is one of the features amongst many offered by Karate Framework.

Eval is a built-in function in Karate that can be used to execute a dynamic sequence of steps. It enables you to execute code dynamically at runtime. This dynamic sequence of steps can be defined in a string or a JSON file, which can be passed to the eval function.

In simple terms, eval allows developers to carry out custom dynamic computations and validations to test their APIs.

What are the Advantages of Using Eval Function in Karate?

There are several advantages of using the eval function in Karate Framework:

• Dynamic execution: Eval function allows us to execute dynamic code or sequence of steps dynamically. It helps the developers to execute validations or custom computations dynamically at runtime.
• Code reusability: With the help of the eval function, we can create custom code blocks that can be reused multiple times within the same testing suit. This helps in reducing the overall test code complexity and improves code maintainability.
• Reuse existing code snippets: With eval, we can execute code snippets that are already present in the test scripts. We can pass any data from the script to the code snippet and execute it on the fly. It helps in reusing the code while keeping test scripts organized.
• Debugging: When writing complex test scripts, it becomes difficult to write tests case by case. With the help of eval function, we can easily debug and execute the code blocks. It allows us to verify the expected results with more precision.

How to Use Eval Function in Karate?

The eval function is written in JavaScript, and it can be used to execute code blocks dynamically. Here is an example of how to use the eval function in Karate:

Suppose we want to execute a simple JavaScript code block using the eval function in Karate. Let’s assume that we have an integer variable which we want to increment by one using the eval function. Here is how we can do it:

Given def count = 0 
When eval count = count + 1 
Then assert count == 1

In the above code, we first set the initial count value to zero. Then we use the eval function to increment the count value. Finally, we assert that the count value has been incremented by one.

What are the Limitations of Using Eval Function in Karate?

While there are several advantages of using eval function in Karate, it also comes with some limitations:

• Security Risks: With the use of eval function, it is possible to execute any code block, which can cause a potential security threat if not well regulated. It is essential to write the code carefully, to avoid any malicious input that may cause an issue.
• Performance Issues: When using eval function, it is important to keep the code as efficient as possible. This is because the dynamic code execution can impact test performance if not optimized correctly.
• Debugging Complexity: While the eval function helps in debugging the test scripts, it can also create more complexity when troubleshooting the scripts to ensure that each block executes as expected.

What is the eval function in Karate Framework?

If you are a developer who is interested in testing web services or APIs, you might have heard of the Karate framework. Karate is an open-source tool that allows developers to write automated tests for web services or APIs. One of the most useful functions in Karate is the „eval“ function. In this blog post, we will explain what the eval function is and how to use it in Karate Framework.

What is the eval function?

The eval function is a built-in function in Karate that allows developers to evaluate an expression in the context of the current Karate scenario. The expression can be any valid Groovy or Java code. The eval function returns the result of the evaluated expression, which can be used in other parts of the Karate scenario.

How to use the eval function

To use the eval function in Karate, you need to follow these steps:

Step 1: Create a Karate scenario

First, you need to create a Karate scenario in which you want to use the eval function. You can create a new scenario or add the eval function to an existing scenario.

Step 2: Call the eval function

Once you have your Karate scenario, you can call the eval function by typing „eval“ followed by a valid Groovy or Java expression inside parentheses. Here is an example:

„`
Given url ‚http://localhost:8080/api/books‘
When method get
Then status 200
And def response = response
And def bookCount = eval karate.jsonPath(response, ‚$.books.length()‘)
And print ‚The number of books is:‘, bookCount
„`

In this example, we are using the eval function to get the number of books in the response of a GET request to „http://localhost:8080/api/books“. We are using the Karate.jsonPath function to extract the length of the „books“ array from the response and assign it to the „bookCount“ variable using the eval function. Finally, we are printing the number of books to the console using the print function.

Step 3: Use the result

You can use the result of the eval function in other parts of your Karate scenario. In our example, we assigned the result to the „bookCount“ variable, which we can use in other assertions or print statements.

Advantages of using the eval function

There are several advantages of using the eval function in Karate:

• Flexibility: The eval function allows you to evaluate any valid Groovy or Java expression, which gives you a lot of flexibility in your testing.
• Reusability: The result of the eval function can be used in other parts of your Karate scenario, which promotes code reuse.
• Readability: The eval function can help make your Karate scenario more readable by allowing you to break complex expressions into smaller, more manageable pieces.

Conclusion

The eval function is a powerful tool for developers who are working with the Karate framework. By allowing you to evaluate any valid Groovy or Java expression, the eval function gives you a lot of flexibility in your testing. It also promotes code reuse and makes your Karate scenarios more readable. Now that you know how to use the eval function, you can start using it in your own Karate scenarios to make your testing more efficient and effective.