Test your API docs!

Today many API docs are driven by API description formats, such as Swagger/OpenAPI, API Blueprint, and so on. I'm working on an Open Source tool (Dredd), which verifies whether the implementation is according to the description. This enables a whole new workflow to API designers - they can design before implementing, and then ensure the implementation is in sync with the design.

https://fosdem.org/2018/schedule/event/test_api_docs_with_dredd/

Transcript

1. Test your API docs!
   It's tested or it's broken
   Honza Javorek
   FOSDEM 2018
   

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2. Honza
   honzajavorek.cz
   @honzajavorek
   

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6. PRAGUE
   

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7. Czech Republic
   

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8. PYCON.CZ
   

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10. Interface of libraries
    #!/usr/bin/env python
    import django
    

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11. Interface of systems
    curl https://api.github.com/
    

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12. Technical?
    

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13. User interface!
    

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14. import urllib2
    gh_url = 'https://api.github.com'
    req = urllib2.Request(gh_url)
    password_manager = urllib2.HTTPPasswordMgrWithDefaultRealm()
    password_manager.add_password(None, gh_url, 'user', 'pass')
    auth_manager = urllib2.HTTPBasicAuthHandler(password_manager)
    opener = urllib2.build_opener(auth_manager)
    urllib2.install_opener(opener)
    handler = urllib2.urlopen(req)
    print handler.getcode()
    print handler.headers.getheader('content-type')
    Do you like this interface?
    

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15. Requests: HTTP for Humans
    

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16. >>> r = requests.get('https://api.github.com/user',
    ... auth=('user', 'pass'))
    >>> r.status_code
    200
    >>> r.headers['content-type']
    'application/json; charset=utf8'
    >>> r.encoding
    'utf-8'
    >>> r.text
    '{"type":"User"...'
    >>> r.json()
    {'disk_usage': 368627, 'private_gists': 484, ...}
    Do you like this interface?
    

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17. How do you design the
    interface?
    

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18. Eating your own dog food
    

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19. def test_basic_building():
    req = requests.Request()
    req.url = 'http://kennethreitz.org/'
    req.data = {'life': '42'}
    pr = req.prepare()
    assert pr.url == req.url
    assert pr.body == 'life=42'
    

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20. Writing tests first
    helps to design the interface
    TDD
    

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21. test > RED > implement > test > GREEN
    req = requests.Request()
    req.url = 'http://kennethreitz.org/'
    req.data = {'life': '42'}
    pr = req.prepare()
    assert pr.url == req.url
    assert pr.body == 'life=42'
    

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22. Writing down behavior first
    helps to design the interface
    BDD
    

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23. Feature: Status code
    Background:
    Given you expect HTTP status code "200"
    Scenario: Different real response status
    When real status code is "500"
    Then Gavel will set some error for "status code"
    And Request or Response is NOT valid
    Scenario: Response status code match
    When real status code is "200"
    Then Gavel will NOT set any errors for "status code"
    And Request or Response is valid
    Gherkin / Cucumber
    

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24. Testable documentation!
    

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25. 1. Design
    2. Test
    3. Implement
    

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26. 1. Think, agree, promise
    2. Test the promise
    3. Fulfill the promise
    

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27. How did Kenneth
    design requests?
    

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29. Before I start writing a single line of code,
    I write the README and fill it with usage
    examples. I pretend that the module I
    want to build is already written and
    available, and I write some code with it.
    “
    https://www.kennethreitz.org/essays/how-i-develop-things-and-why
    

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30. RDD
    

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31. RDD
    Readme Driven Development
    http://tom.preston-werner.com/2010/08/23/readme-driven-
    development.html
    

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32. # Requests
    The `requests` library allows you to perform HTTP
    requests from your Python code.
    ## Example
    ```python
    >>> r = requests.get('https://github.com')
    >>> r.status_code
    200
    ```
    ## License
    MIT
    README.md
    

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33. Readme Driven
    Development
    • chance to think through the project first
    • docs are ready - no need to write them retroactively
    • your team can use the interface before it exists
    • easy to discuss the interface with everyone
    

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34. Interface in README
    =
    Essential interface user expects
    

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35. README must not
    get out of sync with code
    

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36. How do we ensure
    implementation
    matches the design?
    

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37. python -m doctest README.md
    doctest
    

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38. language: "python"
    python:
    - "3.6"
    script:
    - "python -m doctest README.md"
    Continuous Integration
    

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39. 1. Think, agree, README
    2. Test the README
    3. Fulfill the README
    

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40. What if we could design and
    test web APIs like this?
    

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41. # Calendar API
    The API gives you various means to work with date and time.
    ## GET /now
    Provides you with current date and time.
    - Response 200 (application/json)
    ```json
    {
    "day": 29,
    "month": 2,
    "year": 2017,
    "hour": 11,
    "minute": 45,
    "second": 38
    }
    ```
    API.md
    

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44. dredd API.md http://localhost:8000
    Dredd
    

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52. Go
    JavaScript
    Perl
    PHP
    Python Ruby
    Rust
    

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53. language: "python"
    python:
    - "3.6"
    before_install:
    - "npm install -g dredd"
    script:
    - "dredd API.md http://localhost:8000"
    Continuous Integration
    

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56. What about the OpenAPI Spec?
    (fka Swagger)
    

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57. YAML
    

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58. 1. Think, agree, API desc.
    2. Test the API desc.
    3. Fulfill the API desc.
    

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59. Testing implementation against design
    allows you
    designing before implementing
    

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60. Designing before implementing
    allows you
    better design
    

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61. Dredd
    allows you
    better design
    

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62. Remember
    • think first, design first, docs first, test first
    • discuss the the interface design before implementing
    • use the interface before implementing (mocks, tests)
    • have your interface design as a single source of truth
    • test implementation against the design
    

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64. github.com/apiaryio/dredd
    @honzajavorek
    

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