How can I mock a Ballerina HTTP Client when writing Ballerina unit tests?

Question

I'm currently working on writing unit tests for a resource function in an HTTP service in Ballerina. In this resource function, I'm calling HTTP client endpoints dynamically, and I don't have a predefined client for a particular service.

In the Ballerina documentation, there's an example of how to create a mock instance for an HTTP client using test:mock(http:Client), when the external endpoint is already established for a specific service. However, in my case, I need to mock the endpoint dynamically as I don't have a predefined client.

How can I mock the endpoint for the purpose of testing in this scenario?

Answer 1

You can do the dynamic client generation within resource function using functions. These functions should be available at module level.

e.g.

service / on new http:Listener(9090) {
    resource function get values() {
        http:Client client = intializeClient();
        ...
    }
 }

function intializeClient() returns http:Client|error {
   return new ("https://xxxxx/xx/");
}

Then in tests, you can mock this using function mocking and return a test double with the mock behavior. You can refer to https://ballerina.io/learn/test-ballerina-code/test-services-and-clients/ for more details.