Attachments

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Cucumber lets you attach arbitrary data — screenshots, response payloads, logs, links — while a scenario runs. Attachments are recorded against the step (or hook execution) that attached them. Until a step fails they are invisible; a failing step's error output lists everything the scenario attached. When Cucumber Messages output is enabled (config :cucumber, messages: "path.ndjson"), attachments are also emitted as attachment envelopes in the message stream, attributed to their step or hook, where standard Cucumber report tooling can render them.

Attaching data

Cucumber.attach/4 works from any step definition or hook and returns the context unchanged, so it composes with any return style:

step "the API responds", context do
  context
  |> Cucumber.attach(response.body, "application/json")
  |> Map.put(:response, response)
end

Strings are attached as-is. Binary data must be marked explicitly with {:bytes, binary} — Elixir can't tell text from bytes by type — and is Base64-encoded for transport:

step "I take a screenshot", context do
  Cucumber.attach(context, {:bytes, screenshot()}, "image/png",
    filename: "checkout.png"
  )
end

Convenience helpers

# Attach a log message (media type text/x.cucumber.log+plain)
Cucumber.log(context, "user #{user.id} created")

# Attach a link (media type text/uri-list)
Cucumber.link(context, "https://dashboard.example.com/run/123")

Attribution

Each Cucumber.Attachment records where it came from:

  • phase — :step, :before_scenario, or :after_scenario
  • step_text / step_line — the attaching step, when phase is :step (attachments from before_step/after_step hooks attribute to the step they bracket)
  • feature_file / scenario_name — the owning scenario

Attachments from concurrent @async scenarios are recorded safely and keep their own scenario's attribution.

Failure output

When a step fails, its error message ends with the scenario's attachments:

Attachments:

  * text/x.cucumber.log+plain: starting checkout flow
  * image/png (checkout.png): 18432 bytes, base64-encoded