Live Test & Fixture Recording Skill

You write live integration tests that exercise the real GitHub Copilot API and capture responses as JSON fixtures for deterministic replay. This is the project's VCR-like system for ensuring tests stay grounded in real API behavior.

Architecture overview

Live test (mix test --include live --include save_fixtures)
  │
  ├─ RecordingProvider  ← wraps real Copilot provider, captures SSE events
  │     │
  │     └─ persistent_term storage ← events buffered here during stream
  │
  └─ FixtureHelper.save_fixture/2  ← writes events to JSON file
        │
        └─ test/support/fixtures/<name>.json

Fixture-based test (mix test)
  │
  ├─ FixtureProvider  ← reads fixture JSON, replays events via Req.Response.Async
  │     │
  │     └─ FixtureHelper.build_fixture_response/1 ← spawns process to send SSE events
  │
  └─ Assertions on agent behavior, events, tool calls, etc.

When to act

• Adding a new agent behavior that needs a new fixture (e.g., new tool call pattern, multi-turn conversation, error handling).
• Adding or changing provider integration logic.
• When the user asks to "record a fixture", "add a live test", or "capture API responses".
• When an existing fixture is stale and needs re-recording.

Writing a live test

Live tests go in

test/opal/live_test.exs

. They require

@moduletag :live

(excluded by default) and use the

RecordingProvider

to capture real SSE events.

Template

describe "live API — <scenario description>" do
  @tag :save_fixtures
  @tag timeout: 30_000
  test "records <what this captures>" do
    RecordingProvider.start_recording()

    {:ok, pid} =
      Opal.start_session(%{
        model: {:copilot, "claude-sonnet-4"},
        system_prompt: "<constrained prompt that produces deterministic output>",
        tools: [<tool modules if needed>],
        working_dir: System.tmp_dir!(),
        provider: RecordingProvider
      })

    {:ok, response} = Opal.prompt_sync(pid, "<user message>", 25_000)
    Opal.stop_session(pid)

    events = RecordingProvider.stop_recording()
    assert length(events) > 0

    # Save as a fixture for replay
    path = FixtureHelper.save_fixture("<descriptive_name>.json", events)
    assert File.exists?(path)

    # Assertions on the live response
    assert is_binary(response)
    assert String.contains?(response, "<expected content>")
  end
end

Running

# Run all live tests (requires valid Copilot auth)
mix test --include live

# Run live tests AND save recorded fixtures to disk
mix test --include live --include save_fixtures

# Run a specific live test
mix test --include live test/opal/live_test.exs:<line_number>

Writing a fixture-based integration test

Once you have a fixture, write a deterministic integration test that replays it. These go in

test/opal/integration_test.exs

or a new file under

test/opal/

.

Template

describe "<feature under test>" do
  test "<what it verifies>" do
    # Configure the FixtureProvider with your fixture
    :persistent_term.put({FixtureProvider, :fixture}, "<your_fixture>.json")

    # For multi-turn tests (tool call → second response):
    # :persistent_term.put({FixtureProvider, :second_fixture}, "<second_turn>.json")

    session_id = "test-#{System.unique_integer([:positive])}"
    {:ok, tool_sup} = Task.Supervisor.start_link()

    agent_opts = [
      session_id: session_id,
      model: Model.new(:copilot, "test-model"),
      system_prompt: "<system prompt>",
      tools: [<tool modules>],
      working_dir: System.tmp_dir!(),
      provider: FixtureProvider,
      tool_supervisor: tool_sup
    ]

    {:ok, pid} = Agent.start_link(agent_opts)
    Events.subscribe(session_id)

    Agent.prompt(pid, "<user message>")

    # Assert on events received
    assert_receive {:event, %{type: :response_start}}, 5_000
    assert_receive {:event, %{type: :text_delta, data: %{delta: delta}}}, 5_000
    assert is_binary(delta)
    assert_receive {:event, %{type: :response_end}}, 5_000
  end
end

Fixture file format

Fixtures live in

test/support/fixtures/

as JSON:

{
  "description": "Recorded live fixture: responses_api_text.json",
  "recorded_at": "2025-02-13T...",
  "events": [
    {"data": "{\"type\":\"response.created\",\"response\":{...}}"},
    {"data": "{\"type\":\"response.output_item.added\",...}"},
    {"data": "{\"type\":\"response.completed\",...}"}
  ]
}

Each

data

field contains one SSE event payload as a JSON string.

Rules

1. System prompts in live tests must be highly constrained to produce deterministic output. Use prompts like "Respond with exactly the word 'pong'" rather than open-ended prompts.
2. Name fixtures descriptively:

   responses_api_tool_call.json

   , not

   test1.json

   .
3. Never hand-edit fixture JSON. Always re-record from a live test.
4. Tag live tests correctly:

   @moduletag :live

   on the module,

   @tag :save_fixtures

   on recording tests,

   @tag timeout: 30_000

   for API calls.
5. Clean up after recording tests if the fixture is only meant for one-time capture — or keep it permanently if it will be used by replay tests.
6. Fixture-based tests should be fast and async-safe — they replay from disk, no network needed.
7. When adding a fixture for a new scenario (e.g., error response, high token usage), also add a corresponding integration test that replays it.

Key files

• test/opal/live_test.exs

  — Live API tests with recording

• test/opal/integration_test.exs

  — Fixture-based integration tests

• test/support/fixture_helper.ex

  — Fixture load/save/replay helpers

• test/support/fixtures/

  — Recorded fixture JSON files