how do I dynamically generate multiple HTTP mock responses with VCR for Ruby/RSpec?

Question

I'm hitting an API and for each request, there was a recorded request/response in the cassette YAML file. However, the only difference between the requests was the id in the query parameters.

How do I shrink my YAML file so that URLs are dynamically generated for each request?

Answer 1

You can use Dynamic ERB Cassettes with VCR, you just have to pass in the :erb option which can have a value of true or a hash containing the template variables to be passed to the cassette:

ids = [0, 1, 2, 3]
VCR.use_cassette('dynamic_generated_requests', :erb => { :ids => ids }) do
  # Make HTTP Requests
end

YAML File with ERB

And your YAML file would look like this:

---
http_interactions:
<% ids.each do |id| %>
- request:
    method: post
    uri: https://api.example.com/path/to/rest_api/<%= id %>/method
    body:
      encoding: UTF-8
    headers:
      content-type:
      - application/json
  response:
    status:
      code: 200
      message: OK
    headers:
      cache-control:
      - no-cache, no-store
      content-type:
      - application/json
      connection:
      - Close
    body:
      encoding: UTF-8
      string: '{"status_code": <%= id %>}'
    http_version: '1.1'
  recorded_at: Tue, 15 Jan 2019 16:14:14 GMT
<% end %>
recorded_with: VCR 3.0.0

Note: the .yml file extension is still used because VCR handles the ERB processing through the :erb option.

Debugging: raw_cassette_bytes

If you want to debug this and make sure the YAML file looks good, you can print out the rendered YAML file with the raw_cassette_bytes method:

puts VCR.current_cassette.send(:raw_cassette_bytes)

Use that within the VCR.use_cassette block:

VCR.use_cassette('dynamic_generated_requests', :erb => { :ids => ids }) do
  puts VCR.current_cassette.send(:raw_cassette_bytes)
  # Make HTTP Requests
end