How I learned Postman Tests

About me

I am a Java backend developer with 3 years of experience

Why I wanted to learn Postman Tests

It is a good solution for QA engineers when they want to test the backend API, they can create test cases and run test suite. For backend devs, It is a good possibility to test microservices when you rewrite microservices from one to another. I wanted to learn Postman tests, because I have to write the same apps using different languages.

How I approached learning Postman Tests

Firstly before creating tests, we need the server app with API or we can design API and using the mock server in postman. I show you an example model of API below:

1. Create new book (Method: POST; endpoint: /books). When someone wants to create with the same id, the service should return 409 Error
2. Delete book by id (Method: DELETE; endpoint: /books/{id})
3. Read book by id (Method: GET; endpoint: /books/{id}). When someone wants to read book with unexistent id, the service should return 400 Error
4. Update book by id (Method: PUT; endpoint: /books/{id}).When someone wants to update book with unexistent id, the service should return 400 Error

The model of Book:

{
  "id": string,
  "title": string,
  "author": string,
  "publisher": string
}

The Test Cases

For every test case we will create separate request in Postman. It will give us a possibility to run a collection like a list of test cases.

1. Create Book
   
   You can see that for the test case, we have 2 Postmans tests (old approach):

   tests["Status code is 200"] = responseCode.code === 200;
   tests["Body is correct"] = responseBody === pm.environment.get("body")
   

   On Tests Tab we have an access to specific variables like tests, responseCode, responseBody.

   • tests - array of tests, where key is a name of our Postman test;
   • responseCode - object where one parameter is HTTP response code;
   • responseBody - string which contains response object;

   Test Results:
   

2. Get Book By id
   
   You can see that for the test case, we have 4 Postmans tests ( different approach):

       var body = {"id":"123", "title": "Harry Potter", "author": "Rowling", "publisher": "ababahalamaha"};
   
       pm.test("Status code is 200", function () {
           pm.response.to.have.status(200);
       });
   
       pm.test("Status code is ok", function () {
           pm.response.to.have.status("OK");
       });
   
       pm.test("Content-Type is present", function () {
     		pm.response.to.have.header("Content-Type");
       });
   
       pm.test("Body is correct", function () {
           pm.response.to.have.body(JSON.stringify(body));
       });
   

3. Update exist book
   
   You can see that for the test case, we have 4 Postmans tests ( different approach, using response.to.be):

   
     // example using pm.response.to.be*
     pm.test("Status code is 200y", function () {
          // assert that the status code is 200
          pm.response.to.be.ok; // info, success, redirection, clientError,  serverError, are other variants
     });
     pm.test("response must be with Body", function () {
          // assert that the response has a valid JSON body
          pm.response.to.be.withBody;
     });
     pm.test("response must be json", function () {
          pm.response.to.be.json; // this assertion also checks if a body  exists, so the above check is not needed
     });
     pm.test("Body is correct", function () {
         pm.response.to.have.body(pm.environment.get("body"));
     });
   

4. Create Book with Existent Id
   
   You can see that for the test case, we have 3 Postmans tests ( different approach, using pm.expect)

       var result = JSON.parse(responseBody);
   tests["Status code is 409"] = responseCode.code === 409;
   
   
   pm.test("Error is correct", function () {
       var jsonData = pm.response.json();
       pm.expect(jsonData.error).to.eql("Conflict");
   });
   
   pm.test("Message is correct", function () {
       pm.expect(pm.response.text()).to.include("The book with the same id was created before");
   });
   

5. Get Book By non-existent id

   1. Response code equals 404;
   2. Response body has to contain error: "Not Found" and message:"Book with current id is not exist"

   You can try make your own Postman tests.

6. Update non-existent book

   1. Response code equals 404;
   2. Response body has to contain error: "Not Found" and message:"Book with current id is not exist"

7. Delete Book

   1. Response code equals 200;

How to Run All Test Cases

OK, seriously I had big problem with it, collection didn't start!!!))) Seriously)
Don't forgot to save your requests!!!

1. Click button in red below
   

2. Click Run;
   

3. Click Run Book
   
   And Whoallya!!! Our Result!!!

Tips and advice

You need to have basic of JS and don't forget to save your requests))

Final thoughts and next steps

I think in the future you can try to integrate Postman Tests in your CI/CD or you can try to write tests in BDD style.