---
title: "Test for functional behavior | Grafana k6 documentation"
description: "Use k6 to write requests and assert that they respond correctly"
---

# Test for functional behavior

In this tutorial, learn how to write a test that does the following:

- Sends a POST request to the new endpoint
- Creates a check for the response status

## Script the Request

The first thing to do is to add logic for the endpoint. To do that, you need to make an [HTTP request](/docs/k6/latest/using-k6/http-requests/):

1. Import the HTTP module.
2. Create a payload to authenticate the user.
3. Use the [`http.post`](/docs/k6/latest/javascript-api/k6-http/post/) method to send your request with the payload to an endpoint.

To test, copy this file and save it as `api-test.js`.

JavaScript ![Copy code to clipboard](/media/images/icons/icon-copy-small-2.svg) Copy

```javascript
// import necessary module
import http from 'k6/http';

export default function () {
  // define URL and payload
  const url = 'https://quickpizza.grafana.com/api/users/token/login';
  const payload = JSON.stringify({
    username: 'default',
    password: '12345678',
  });

  const params = {
    headers: {
      'Content-Type': 'application/json',
    },
  };

  // send a post request and save response as a variable
  const res = http.post(url, payload, params);
}
```

Run the script using the `k6 run` command:

Bash ![Copy code to clipboard](/media/images/icons/icon-copy-small-2.svg) Copy

```bash
k6 run api-test.js
```

After the test finishes, k6 reports the [default result summary](/docs/k6/latest/results-output/end-of-test/#the-default-summary).

Bash ![Copy code to clipboard](/media/images/icons/icon-copy-small-2.svg) Copy

```bash
          /\      |‾‾| /‾‾/   /‾‾/
     /\  /  \     |  |/  /   /  /
    /  \/    \    |     (   /   ‾‾\
   /          \   |  |\  \ |  (‾)  |
  / __________ \  |__| \__\ \_____/ .io

  execution: local
     script: api-test.js
     output: -
  ...
```

As an optional step, you can log the response body to the console to make sure you’re getting the right response.

JavaScript ![Copy code to clipboard](/media/images/icons/icon-copy-small-2.svg) Copy

```javascript
export default function () {
  // ...

  const res = http.post(url, payload, params);

  // Log the request body
  console.log(res.body);
}
```

## Add response checks

Once you’re sure the request is well-formed, add a [check](/docs/k6/latest/using-k6/checks/) that validates whether the system responds with the expected status code.

1. Update your script so it has the following check function.

JavaScript ![Copy code to clipboard](/media/images/icons/icon-copy-small-2.svg) Copy

```javascript
// Import necessary modules
import { check } from 'k6';
import http from 'k6/http';

export default function () {
  // define URL and payload
  const url = 'https://quickpizza.grafana.com/api/users/token/login';
  const payload = JSON.stringify({
    username: 'default',
    password: '12345678',
  });
  const params = {
    headers: {
      'Content-Type': 'application/json',
    },
  };

  // send a post request and save response as a variable
  const res = http.post(url, payload, params);

  // check that response is 200
  check(res, {
    'response code was 200': (res) => res.status == 200,
  });
}
```

1. Run the script again.

Bash ![Copy code to clipboard](/media/images/icons/icon-copy-small-2.svg) Copy

```bash
k6 run api-test.js
```

1. Inspect the result output for your check. It should look something like this.
   
   ![Copy code to clipboard](/media/images/icons/icon-copy-small-2.svg) Copy
   
   ```none
   ✓ response code was 200
   ```

> Note
> 
> Under larger loads, this check will fail in some iterations. **Failed checks do not stop tests.**
> 
> Rather, k6 tracks the success rate and presents it in your [end of test](/docs/k6/latest/results-output/end-of-test/) summary.

## Next steps

In this tutorial, you’ve used k6 to make a POST request and check that it responds with a `200` status.

However, these tests make only one request, which doesn’t say much about how the system will respond under load. For that, you need to [test under load](/docs/k6/latest/examples/get-started-with-k6/test-for-performance/).