I presented this topic at "The Test Tribe Community" meet up on 27/11/2021 with a live demo. This presentation will be a good starting point if you need to start writing simple and meaningful tests in Postman.

1. API Testing - The
Power of Libraries
Anuradha Raman

2. Anuradha Raman
★ Lead Automation Test Engineer
@Kissflow
★ 10+ years of experience in
software testing
★ Test Tribe champion for the
Chennai Chapter

3. Outline
➢ API Test Strategy
➢ Designing test scenarios for API testing
➢ Writing tests in Postman using different libraries

4. API Testing
Objectives:
● To ensure that the business logic implementation is working correctly as
expected
● To ensure that the implementation is working as specified according to the
requirements specification (API documentation)
● To prevent regressions between code merges and releases

5. API Testing - Scenarios
Positive Scenario
Negative Scenario
Flow Based - Series of requests which are common user actions or use
cases
Test every single API for
different sets of valid and
invalid input test data

6. Postman - A collaboration platform for
API development
● Collaborate in real-time with built-in version control
● Directly send REST, SOAP, and GraphQL requests
● Generate beautiful, machine-readable documentation
● Provide a shared context for building and consuming APIs
● Simulate endpoints and responses without having to set up a backend server

7. API Testing in Postman
a. Request level
Functional -> Request-Response Validation
Automated -> Code snippets -> Basic response code and response
object validation
a. Collection level tests
b. Schema validation test (https://ajv.js.org/)
pm.test("Response uses a valid schema", function() {
pm.expect(ajv.validate(cam, SCHEMA_STORED_AS_A_VARIABLE)).to.be.true;
});

8. Writing Tests in Postman
➔ Pre Request Tab (before)
➔ Tests (after)
➔ Assertions
◆ Parse the response body
◆ Write test script
Javascript code can be
written in both these places

9. JSON - JavaScript object notation
JSON String:
‘{
“Name”:”value”,
“array”: [ ]
}’
★ Data is in name value pairs
★ Data is separated by commas (,)
★ Curly braces holds objects
★ Square braces holds arrays
https://jsonpath.
herokuapp.com/

10. Variables
- Dynamic Variables using Faker library
(https://www.npmjs.com/package/faker)
- Generate mock/dummy test data for each run
- Some interesting dummy variables to note :
- Random filenames,
- images,
- catchphrases,
- To use in pre request and tests tab
pm.variables.replaceIn.(“{{$randomFirstname}}”)

11. Chai
Chai Assertion Library BDD: Default library in postman for assertions
This syntax provides options to optimize how readable (expect and should)
your tests are to you and your collaborators
const jsonData = pm.response.json(); -->Parsing the response body
pm.test("response data not null", function () {
pm.expect(jsonData.page).to.be.an('number');
pm.expect(jsonData.per_page).to.be.an('number');
pm.expect(jsonData.total_count).to.be.an('number');
pm.expect(jsonData.data.length).to.be.above(0);
})
Chai Assertion

12. Cheerio - Moment - Lodash
Cheerio - To parse HTML
response
Moment - working with dates Lodash - for loop
● To parse and retrieve the value
from an HTML response, we will
use the cheerio JavaScript library
● Simple library for working with the
DOM model.
● Cheerio wraps around parse5
parser and can optionally use
htmlparser2.
https://cheerio.js.org/
https://blog.logrocket.com/parsing-html-
nodejs-cheerio/
https://github.com/cheeriojs/cheerio
● To work with “dates” in Postman
● Can be used to manage test data in
pre requests tab or even query
params
https://momentjs.com/docs/
● Use with pm.expect() =>iterating
through response data, to help
assert that a certain value is
present.
● create some dynamic data to use in
our requests => The ‘_.random()’
Lodash function syntax
(_random(1000))
https://lodash.com/docs/4.17.15#forEach

13. Debugging Test Failures
● console.log(),
● console.info(),
● console.warn()
● and console.error()
=> Debug statements with test assertions,
=> Examine the content of the HTTP requests and responses, as well as Postman data
items such as variables

14. Automated tests in Postman
1. Workflows/End to End Testing/User Journey
2. Workflows=>Collection of API Requests. Automating workflows with the
collection runner
3. Default execution of requests in a Postman collection is sequential/linear
4. Configure which request to run next using pm.setNextRequest();
5. Loop over current request => Set name of current request to setNextRequest
6. Stop the run => pm.setNextRequest(null);

18. A perfect working API leads to the perfect working application

19. Thank you