Mastering Karate in Five Steps - Step 2: Variables, karate-config, API requests, Assertions

Second step of the Karate Framework Usage; Variables, Requests Assertions

Step-2: Variables, karate-config, API requests, Assertions

In this article, I will be talking about variables and simple API requests with Karate Framework. In the first part, I talked about introducing Karate and did a simple setup.


>>If you haven't read the first part of this series yet, click here!


If you don't have any previous experiences with BDD, you can refer to this article about what the BDD is and its usage. Now, let's continue with the variables in Karate.


 You can define the variables with the def keyword in the feature file directly. The structure should be a def keyword followed by a variable name and a value. It is like defining variables in any programming language. Here is the one simple usage of the variables.

Scenario: this scenario is for defining variables
 * def firstVariable = 12
 * def secondVariable = 'cakes'
 * print 'firstVariable -> ' + firstVariable, 'secondVariable -> ' + secondVariable

Output of the above scenario is: 

10:42:56.259 [ForkJoinPool-1-worker-1] INFO - [print] firstVariable -> 12 secondVariable -> cakes

In the example above, I have shown you the simple usage of the variables. But in the API testing, you need to define a complex JSON object and do your operations with this JSON object. Now, let's create a JSON object in the feature file and print it. 

Scenario: defining JSON object and print it
    Given def jsonObject =
            "name": "jack",
            "phone" : 15435667788
            "name": "jennie",
            "phone" : 13443567234
    * print jsonObject[1].name, jsonObject[1].phone


And here is the console output: 

10:45:05.097 [ForkJoinPool-1-worker-1] INFO - [print] jennie 13443567234

As you see, it is convenient and practical. You are not responsible for any operations back other than writing Gherkin syntax. 



You will need to have some files that you can write for centralized data. You can use the karate-config.js file to write your global variables like base URL, environment, etc. Here is the template of the karate-config.js file:

function fn() {   
 var env = karate.env; // get system property 'karate.env'
 karate.log('karate.env system property was:', env);
 if (!env) {
   env = 'dev';
 var config = {
   env: env,
   myVarName: 'hello karate',
   baseUrl: ''
 if (env == 'dev') {
   // customize
   // e.g. = 'bar';
 } else if (env == 'e2e') {
   // customize
 return config;

This is a simple JS function. You can define the variables in the config as a JSON format (“key: value” structure) and use this variable name directly in the feature file. Also, you can define variables based on the environment that you may want to specify different values. In the example below, you will see a basic usage of the karate-config.js file above.

Scenario: using karate-config
 * print baseUrl
 * print myVarName

And the console output is:

11:04:08.750 [ForkJoinPool-1-worker-1] INFO - [print]
11:04:08.753 [ForkJoinPool-1-worker-1] INFO - [print] hello karate


>>> Click to download the Karate CheatSheet


API basics

Briefly, the goal of doing API testing is sending requests to some services and matching the response, and validating the result. So I can say that your first task is sending a request, and the second one is to verify the response. Let's see what you need to know for sending requests, how to send a request on Karate, then learn the assertions later.

Base URL

You can define the base URL in Karate with the <url> keyword. Just write the url then base URL after that.

Given url ''


Path Params

After you define the URL, you need to define a path to send a request. You can handle path parameters with the path keyword in Karate. 

And path 'blog'


Query Params

Some endpoints present query parameters to search for specific keywords. Here is the usage of the query params in Karate:

And path 'blog'
And param search = 'karatePosts'


GET Request

You can read the data from the API with a get request. Here is the simple get request with Karate.

Scenario: Get request
 Given url ''
 And path 'blog', 'karate'
 When method GET
 Then status 200

Did you notice the last line of the test? In Karate, you can easily verify the status code of the response with the status keyword. I will explain the rest of the assertions below, but you can use the example above for status verification right now. 

I want to show you this GET request with Java and Ruby so that you can compare all of them and see how Karate is more practical than others.

    public void testSomeTest(){
        baseURI = "";
        Response response = given().
                                pathParam("key", "karate").
        assertEquals(response.statusCode(), 200);

Java simple get example

def testSimple
  api_url = ""
  path = "blog"
  resp = HTTParty.get(api_url + path, headers: { })
  resp.code.should == 200

Ruby simple get example

As you see the example above, if we compare Karate and other languages, we can easily say that Karate's coding is very straightforward.

POST Request

You can create new data on the services with a post request. In Karate, you can use the request keyword to attach the request body to your request and method post for sending requests.

Scenario: Post request
 * def user =
     "name": "Jane",
     "username": "jane_pool",
     "phone": 12546758485

 Given url ''
 And request user
 When method POST
 Then status 201

PUT Request

You can use the put method just like a post request and update the data.

Scenario: Put request
 * def user =
     "name": "Jane",
     "username": "jane_forest",
     "phone": 12546758485

 Given url ''
 And path 'user', 129
 And request user
 When method PUT
 Then status 200

DELETE Request

You can remove data with a delete request, and the method delete keyword will handle this request.

Scenario: Delete request
 Given url ''
 And path 'user', 129
 When method DELETE
 Then status 204

As you see in the examples above, you can easily send your API requests with the Karate framework without doing anything other than writing your test scripts with Gherkin syntax. 


As a tester, you are responsible for verifying responses and making related assertions. I have shown you one of the assertions, status verification, but there are many Karate Framework assertions available. You can handle all verifications with 'match' keywords. I will show you some of them now. 

Scenario: Matchers examples
 * def jsonBody =
 "category": {
    "id": 1,
    "name": "cats"
 "name": "kitty",
 "photoUrls": [
 "tags": [
     "id": 0,
     "name": "sweet"
 "status": "available"
 Given url ''
 And path 'pet'
 And request jsonBody
 When method POST
 Then status 200
 And match response.category == jsonBody.category
 And match == '#present'
 And match ==
 And match responseHeaders['Date'] == '#notnull'
 And match each response.tags == { 'id': '#number', 'name': '#string'}

‘#present’ is for verifying data is present or not. 

‘#notnull’ is for checking if the data is null or not. You can also use ‘#null’

‘#number’, ‘#string’ will verify the data types.

each will loop all the responses values if the response includes an array. So you can easily verify all of the values in the response body. 

It is just like talking to someone. Quite easy. These matching examples are only some examples of assertions; more matches are featured in Karate to use in your test scripts. 

This article introduced the simple usage of Karate. The following article will discuss more complex operations like reading data files, callers, and scenario outline structures


Click here to read Karate Framework Step-3


Stay on the line and keep learning...


Selcuk Temizsoy

Experienced Software Test Automation Engineer working in different industries. Software Test Consultant at kloia