# `Excessibility.TelemetryCapture`
[🔗](https://github.com/lessthanseventy/excessibility/blob/v0.18.1/lib/telemetry_capture.ex#L1)

Telemetry-based automatic snapshot capture for LiveView tests.

Attaches to Phoenix LiveView telemetry events to automatically capture
snapshots when LiveView events occur, with no test code changes required.

# `attach`

Attaches telemetry handlers for automatic snapshot capture.

Call this before running tests to enable auto-capture.

# `clear_snapshots`

Clears all captured snapshots.

# `detach`

Detaches telemetry handlers.

# `ecto_query_events`

The Ecto `[..., :query]` telemetry events for the configured `:ecto_repos`.

# `flush_ecto_queries`

Returns and clears the Ecto queries accumulated in the current process
since the last flush, oldest first. Called at each captured event so
queries are attributed to the event that ran them.

# `get_snapshots`

Retrieves all captured snapshots and clears the table.

# `handle_event`

Handles telemetry events and captures snapshots.

# `on_mount`

An **opt-in** `on_mount` hook that records a LiveView's `handle_info`
messages as timeline events.

Phoenix LiveView emits telemetry for `mount`/`handle_params`/`handle_event`/
`render` but not for the message-driven callbacks, so there is no global
event to attach to (issue #147). This hook is the seam: it uses
`Phoenix.LiveView.attach_hook/4` on the `:handle_info` stage, which does
need to be installed per LiveView — so it is opt-in, never forced.

Wire it wherever you want that coverage — a router `live_session` covers
every route in the session in one line:

    live_session :default, on_mount: [Excessibility.TelemetryCapture] do
      # ...routes...
    end

or your web module's `live_view/0` to cover every LiveView. It attaches
nothing unless telemetry capture is running (`mix excessibility.debug`) and
the socket is connected, so it is safe to leave wired in all environments.
Pair it with the (also opt-in) `message_flooding` analyzer.

# `write_snapshots`

Writes captured snapshots to timeline.json.

Note: HTML snapshot files are NOT generated from telemetry capture.
For real accessibility testing, use `html_snapshot(view)` in your tests
to capture actual rendered HTML.

Runs in the `on_exit` installed by `use Excessibility`, so a failure
here is logged rather than raised — instrumentation must not fail the
test it observes.

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*Consult [api-reference.md](api-reference.md) for complete listing*