Mocking with examples

Let’s take a deep dive into how mock servers and examples work together, and how you can integrate them into your workflow for a more enhanced API experience with Postman.

1. Sending a request (R1)
2. Saving the request (R1) to a collection (C1)
3. Saving the request R1’s response as an example (P1)
4. Creating a mock (M1) for the collection (C1)
5. Sending a request using the mock server (M1)

Setting up some basics

Before we get into the details of mocking, let’s start with setting up some basics required for mocks to work:

Step 1: Sending a request (R1)

From the Postman app, send a GET request to the URL https://postman-echo.com/get?test=123. This request hits the Postman Echo service which you can use to test out your REST clients and make sample API calls.

The resulting response can be seen on the right, and a record of this request will now be visible in your history on the left.

Step 2: Saving the request (R1) to a collection (C1)

Hit the Save button to open the SAVE REQUEST modal. Collections are simply groups of requests that can be connected together to create APIs and workflows.

You can save a request to an existing collection, or save it to a new collection. Let’s create our new collection called C1.

Collection C1 will now be accessible in the Collections tab in the application. We can do all sorts of things within the collection details view: viewing API documentation, mocking a collection, monitoring a collection, or running the collection.

Step 3: Saving the request R1’s response as an example (P1)

Now, let’s save an example response from the request we just sent by hitting the Save Responsebutton.

This takes us to the Examples screen which can be used to save the request response as an example. Let’s call this example P1.

Enter a name for this example. The request method, URL, and status code are crucial in determining which responses will be returned by the mock we will create. Verify these elements are all as desired, and hit the Save Example button. Hit the back arrow in the top left to return to the request builder, and we can now see the example we created in the top right, added to the request.

Mocking with examples

In the previous steps, we prepared the collection, request, and example response necessary for us to get started with mocking. So let’s continue with the next steps.

Step 4: Creating a mock (M1) for the collection (C1)

There are two ways to create a mock for our collection: 1) using the Postman app and 2) using the Postman Pro API. In this example, we will mock a collection using the Postman app.

From the Postman app, click on the right angle bracket (>) next to the collection you wish to mock to expand the collection details view.

Under the Mocks tab, click the Add a mock link to open the MOCK COLLECTION modal. Here, you can choose a corresponding environment to include in your mock.

We are not using any environment variables in our single saved example (P1), therefore we are going to go ahead and create a mock with No Environment chosen. It’s important to note that if your saved example has an environment variable in the URL, for example, /my/path and you do not provide the corresponding environment when creating the mock, trying to mock that particular request will not work.

Once you mock the collection, it will be visible under the Mocks tab of the collection details view. You can also see the mock URL we will need for the next step.

Step 5: Sending a request using the mock server (M1)

Now that we have created our mock M1, let’s try sending a request to this mock endpoint. Copy the mock URL from the mock we created in the previous step, and paste it into a new request, with an undefined path in this case https://b75a340e-4268-4b20-8f5f-3cfc8f37cec6.mock.pstmn.io. Under the Headers tab of this new request, add the x-api-key header, with the value of your Postman Pro API key.

Sending a request to this mock endpoint with an undefined path returns an error. As you can see, there is no matching saved example with the path '' and the request method GET. Responses returned by the mock service are entirely dependent on your saved examples and the included URL and request method type.

We do, however, have a saved example with the path /get and the request method GET. So sending a GET request to the URL https://b75a340e-4268-4b20-8f5f-3cfc8f37cec6.mock.pstmn.io/get will return the proper response we are looking for.

Adding more examples

To further illustrate how responses from the mock service are entirely dependent on your saved examples, let’s try adding another example to this collection. We’ll repeat steps 1 to 3 of saving the request to a collection and saving the response as an example, with a new URL https://postman-echo.com/test.

Sending a GET request to https://postman-echo.com/test returns a 404 error which we will then save as another example. Our collection C1 now has two requests and two saved examples:

• GET > /get
• GET > /test/

Mocking the /test mock path also gives us our expected 404 response.

Your examples might vary depending on the URL endpoint, request method type, or status code. If you have multiple examples saved to the same mock, you can choose to save each example under a unique URL endpoint like we saw in this example with /get and /test. Alternatively, if you have saved examples with different response status codes, you can send an authenticated request to the mock endpoint along with the x-mock-response-code header specifying which specifies which integer response code your returned response should match.

Learn more about the matching algorithm for mocks.

And we’re done! We have walked through how to create a collection, save requests, save examples, create a mock, and use a mock.