RSpec matcher to test JSON API Controller output provided with ActiveModel Serializer.

render_serialized_json_data.rb

# Encountered an error when tested console output:
#
# ActiveModelSerializers::Adapter::JsonApi::PaginationLinks::MissingSerializationContextError:  JsonApi::PaginationLinks requires a ActiveModelSerializers::SerializationContext.
#  Please pass a ':serialization_context' option or
#  override CollectionSerializer#paginated? to return 'false'.

# Usual RSpec matcher definition
RSpec::Matchers.define :render_serialized_json_data do |expected|
  match do |actual|
    # Prepairing serialized JSON from ActiveRecord(s)
    expected = ActiveModelSerializers::SerializableResource
      .new(expected, {
      # The next line is to provide pagination outside Controller
      :serialization_context => ActiveModelSerializers::SerializationContext.new(request, {})
    }).as_json.to_json

    # actual is expected to be 'response.body'
    expect(actual).to eq expected
  end

  description do
    "render serialized json data"
  end

  diffable
end