TWIL 2020-03-20

Welcome to this week's TWIL session, where our resident expert Katie shares insights on Postman Environments, Variables, & Faker as well as the utility of Postman Pre-Request Scripts. Grasp the power of Postman's environment management and dynamic data generation to enhance API testing efficiency. Katie's contributions this week provide a practical walkthrough on configuring Postman to seamlessly switch API contexts and exploit its dynamic variable feature to simulate real-world data. Furthermore, learn how to leverage pre-request scripts to automate setup and testing processes, ensuring your requests are executed in the exact environment state required. Join us on a journey of micro-learning with Postman's tools that promise to refine your software development practices.

Postman Environments, Variables, & Faker

Our collections often rely on Postman's environments and environment variables (e.g., using base_url in request URLs so that requests can easily switch between APIs), but there is a lot that can be done with Postman's environments, variables, and dynamic variables (powered by Faker).

To access an environment variable in a pre-request script or test:

pm.environment.set("variable_name", "I'm set in the environment now!");
pm.environment.get("variable_name");

This can be used to set and use local variables as well (including, for example, between a pre-request script and test):

pm.variable.set("local_variable_name", "I'm specific to the request I'm in.");
pm.variable.get("local_variable_name");

Postman has dynamic variables that are evaluated in the request:

// request body
{
	"name": "{{$randomName}}",
	"email": "{{$randomEmail}}",
	"favoriteColor": "{{$randomColor}}"
}

// pre-request script / test
pm.variables.set("notes", "{{$randomLoremParagraph}}")

If you need to access the value of an evaluated dynamic variable (since otherwise each instance will be different), you can use replaceIn:

let firstName = pm.variables.replaceIn("{{$randomFirstName}}");
let lastName = pm.variables.replaceIn("{{$randomLastName}}");
let fullName = `${firstName} ${lastName}`;
// "{{$randomFirstName}} {{$randomLastName}}" would result in a full name with a 
// different first and last name than set for firstName and lastName

• https://learning.postman.com/docs/postman/variables-and-environments/variables/

• https://learning.postman.com/docs/postman/variables-and-environments/variables/#variable-scopes

• https://postman-quick-reference-guide.readthedocs.io/en/latest/dynamic-variables.html

Katie Linero

Senior Software Engineer

Postman Pre-Request Scripts

Postman's pre-request scripts can be helpful for a variety of setup, running, and testing uses. For example, ensuring that a given user is logged in (or out) before a request is sent, creating a record specifically for a deletion request, or setting a variable for use in a request based on some API response, all without depending on any other Postman requests.

Logging In

+ Storing Tokens

pm.sendRequest({
    url: `${pm.environment.get("base_url")}/login`,
    method: "POST",
    body: {
        mode: 'raw',
        raw: JSON.stringify(
            {
	            "email": pm.environment.get("user_email"),
	            "password": pm.environment.get("password")
            }
        )
    }
}, function (err, res) {
    let response = JSON.parse(res.json());
    pm.environment.set("access_token", response.tokens.access_token);
    pm.environment.set("refresh_token", response.tokens.refresh_token);
});

Clearing Stored Tokens

pm.environment.set("access_token", "");
pm.environment.set("refresh_token", "");

Creating for Deletion

+ Setting Local Variable for Request URL

// If the request returns the deleted object, saving the creation values in local
// variables can be utilized for testing the response; it may not be useful otherwise
let thingName = "{{$randomNoun}}"
pm.variables.set("thing_name", thingName);

// Create thing for deletion
pm.sendRequest({
    url: `${pm.environment.get("base_url")}/api/things`,
    method: "POST",
    header: {
        "Authorization": `Bearer ${pm.environment.get("access_token")}`
    },
    body: {
        mode: 'raw',
        raw: JSON.stringify({ "name": thingName })
    }
}, function (err, res) {
		// Set local variable `delete_id` for use in request URL
    let response = JSON.parse(res.json());
    let thingId = response.data.id;
    pm.variables.set("delete_id", thingId);
});

Then, our delete request URL can be something like this, without needing to maintain delete_id in the environment or having worry about which records are being/have already been deleted:

{{base_url}}/api/things/{{delete_id}}

• https://learning.postman.com/docs/postman/scripts/pre-request-scripts/

Katie Linero

Senior Software Engineer