Usage

Start each test with the Phoenix (:phoenix) or Playwright (:playwright) backend and keep the rest focused on the user's journey. Most application tests should run once. The Phoenix backend automatically selects the Static (Phoenix.ConnTest) or LiveView (Phoenix.LiveViewTest) driver for each page and can transition between them as the user navigates. Use Playwright when the behavior depends on JavaScript or other browser-owned capabilities.

Your first test

Import the actions, locators, and expectation constructors, and keep session startup in a small test helper. Always import Fluffy.Expect: the enclosing expect(...) call makes an additional Expect. prefix redundant.

defmodule MyAppWeb.ChamberAccessTest do
  use ExUnit.Case, async: true

  import Fluffy
  import Fluffy.Expect
  import Fluffy.Locator

  alias Fluffy.Page
  alias Fluffy.Playwright

  setup context do
    Fluffy.Test.setup(context)
  end

  defp start_app_session(backend \\ :phoenix), do: start_session(backend)

  test "opens the Chamber of Secrets" do
    start_app_session()
    |> visit("/chamber")
    |> fill(by_label("Student"), "Hermione Granger")
    |> fill(by_label("Password"), "parseltongue")
    |> click(by_role(:button, name: "Open chamber"))
    |> expect(visible(by_text("The chamber is open")))
    |> expect(Page.to_have_url("/chambers/secrets"))
  end
end

Page-specific assertions live on Fluffy.Page, which keeps them discoverable separately from locator expectations:

alias Fluffy.Page

session
|> expect(Page.to_have_title("Chamber of Secrets"))
|> expect(Page.to_have_title(~r/^Chamber/))
|> expect(not_(Page.to_have_title("Chamber sealed")))

Title expectations follow Playwright's retrying, whitespace-normalized toHaveTitle behavior. On LiveViews they also observe later @page_title updates.

URL expectations use the same page namespace. Strings and regular expressions match the complete canonical URL. Use the structured form when query serialization order is not part of the contract:

session
|> expect(Page.to_have_url(path: "/potions"))
|> expect(
  Page.to_have_url(
    path: "/potions",
    query: %{"state" => "brewing", "ingredient" => ["lacewing", "boomslang"]},
    query_mode: :subset
  )
)

The path-only form ignores query and fragment. Structured queries decode like URLSearchParams: distinct parameter-name order is ignored, repeated values remain ordered, and subset mode permits unrelated names.

Every operation returns the updated Fluffy.Session, so an ordinary Elixir pipeline represents the user's journey. The lifecycle established by Fluffy.Test.setup/1 closes every session when the test finishes.

The example assumes config :fluffy, endpoint: MyAppWeb.Endpoint in config/test.exs. Fluffy derives the base URL from the endpoint. Explicit session options remain available for tests that target another endpoint or origin.

Every Fluffy test calls Fluffy.Test.setup/1, whether or not the application uses Ecto. When ecto_repos are configured, the same callback also establishes sandbox ownership. See Installation and runtime for endpoint and sandbox configuration.

Choosing a backend

Use :phoenix for the common case: rendered controller pages, forms, LiveViews, links, redirects, cookies, and LiveView events. Its first visit selects the Static or LiveView driver. Later document navigations select the driver for the new page again without changing the public session.

The LiveView driver synchronizes form mutations eagerly: fill, check, uncheck, and select_option immediately dispatch an applicable phx-change and reconcile the server render before returning. It deliberately ignores phx-debounce and phx-throttle, as PhoenixTest does. Choose Playwright when the test is about delayed or blur-only delivery, coalescing, cancellation, or throttle suppression rather than the resulting application state.

Use :playwright when the behavior depends on JavaScript, browser layout, native-validation events or blocking, dialogs, request/response events, or another capability shown as unavailable on Phoenix. With the helper above, the choice is local to the test:

test "updates the preview rendered by a JavaScript hook" do
  start_app_session(:playwright)
  |> visit("/creatures/new")
  |> fill(by_label("Name"), "Basilisk")
  |> expect(visible(by_text("Preview: Basilisk")))
end

A Playwright session owns an isolated BrowserContext. Create another session for another isolated user; pages opened inside one session share that user's cookies and storage.

Application suites run each scenario once. Give it the backend its behavior requires. Paired Phoenix and Playwright runs belong to Fluffy's internal conformance suite; they prove the library's portability contract without duplicating consumer tests.

The full boundary is listed in the capability matrix.

Locators

Prefer locators that describe the interface as a user experiences it:

Use a label for a form control.
Use a role and accessible name for an interactive element.
Use visible text for rendered content.
Use a test ID when user-facing names are ambiguous.
Use CSS for structure that has no user-facing identity.

session
|> fill(by_label("Creature name"), "Basilisk")
|> click(by_role(:button, name: "Register"))
|> expect(visible(by_text("Creature registered")))

Locators are values, so they can be scoped and reused:

potions = by_css("#potions")
potion = by_role(potions, :row, name: "Polyjuice Potion")

session
|> click(by_role(potion, :button, name: "Inspect"))

Available constructors are by_role, by_text, by_label, by_placeholder, by_alt_text, by_title, by_test_id, and by_css. Refine a locator with filter, first, last, or zero-based nth.

Single-target actions are strict: if a locator matches more than one element, Fluffy reports the ambiguity instead of choosing for you. Narrow the locator, or use expect(count(locator, n)) when multiple matches are the intended assertion.

Actions and expectations

Actions and expectations use the same API on both backends:

session
|> visit("/creatures/fluffy")
|> fill(by_label("Keeper"), "Rubeus Hagrid")
|> check(by_label("Flute ready"))
|> select_option(by_label("Status"), "Asleep")
|> click(by_role(:button, name: "Save creature"))
|> expect(enabled(by_role(:button, name: "Save creature")))
|> expect(disabled(by_label("Species")))
|> expect(value(by_label("Keeper"), "Rubeus Hagrid"))
|> expect(editable(by_label("Keeper")))
|> expect(checked(by_label("Flute ready")))
|> expect(visible(by_text("Creature saved")))

Use checked(locator, checked: false) for an unchecked control. The browser-owned indeterminate state is Playwright-only:

session
|> expect(checked(by_label("All ingredients"), indeterminate: true))

Static and LiveView raise Fluffy.CapabilityError for indeterminate state instead of guessing about a DOM property that only application JavaScript can set.

LiveView expectations observe fresh renders and retry transient missing or actionability failures until their deadline. Static expectations are immediate. Playwright uses the browser's native waiting behavior. Pass timeout: to an action or expectation when a particular operation needs a different deadline.

Use submit(form_locator) when the intent is native form submission without a specific submitter. Click the intended submit button when its name=value or override attributes matter. press(locator, "Enter") is reserved for the documented implicit-Enter default action, not as shorthand for submit. The Playwright driver applies native constraint validation; the Static and LiveView drivers deliberately bypass it and submit the current structural form state.

On a LiveView page, the shared Enter, Space, and Tab actions also deliver plain or JS.push-only phx-keydown/phx-keyup bindings. phx-key filtering, window bindings, phx-target, current values, and default-action ordering are covered by the paired browser corpus. Use Playwright for modified key chords, repeat or debounce timing, custom LiveSocket metadata, inline listeners, and bindings that run client-side JS commands such as JS.dispatch.

Files and uploads

The same public action covers ordinary multipart forms and the supported managed LiveView upload lifecycle:

session
|> set_input_files(by_label("Evidence"), ["diary-front.pdf", "diary-back.pdf"])
|> click(by_role(:button, name: "Upload"))

The path list preserves selection order. Pass [] to clear the input. Use a typed in-memory payload for generated bytes or a remote browser:

payload = %Fluffy.FilePayload{
  name: "potion-ledger.csv",
  bytes: "potion,vials\nSleeping Draught,3\n",
  content_type: "text/csv"
}

session
|> set_input_files(by_label("Report"), payload)
|> click(by_role(:button, name: "Upload"))

One path or payload, a homogeneous list of either, and [] are accepted. Fluffy validates and snapshots the complete selection before changing the page. The aggregate default is 10 MB; configure :file_input_max_bytes or pass max_bytes: for one action. Error messages and diagnostic artifacts do not copy payload contents.

Playwright can also capture a script-opened chooser before the triggering click. Pass its result key to set_input_files/4; see Advanced events and pages.

Reloading

Use reload/1 to reload the active document:

session
|> visit("/chambers/secrets")
|> expect(visible(by_role(:heading, name: "Chamber of Secrets")))
|> reload()
|> expect(visible(by_role(:heading, name: "Chamber of Secrets")))
|> expect(Page.to_have_url("/chambers/secrets"))

The Phoenix backend dispatches the current URL again and selects the driver for the returned document. The Playwright backend uses the page's native reload. reload/1 promises a fresh document, not preservation of unsaved client-side state.

Browser-only evaluation

Use Fluffy.Playwright.evaluate/2 when a Playwright test needs a value from the active page:

session
|> then(fn session ->
  data_url =
    Playwright.evaluate(
      session,
      "document.querySelector('canvas').toDataURL()"
    )

  assert data_url =~ "data:image/png"
  session
end)
|> click(by_role(:button, name: "Reveal diary message"))

evaluate/2 returns the JavaScript result, not the session. Use then/2, as above, to continue a pipeline. Function-style expressions can pass is_function: true and arg:. Phoenix sessions raise a capability error instead of pretending to execute client code.

Browser diagnostics

Start a context-wide trace explicitly when debugging a Playwright scenario:

start_app_session(:playwright)
|> Playwright.trace(open: false)
|> visit("/potions/polyjuice")
|> step("Brew Polyjuice Potion", fn session ->
  session
  |> fill(by_label("Boomslang skin"), "3 measures")
  |> click(by_role(:button, name: "Brew"))
end)

Fluffy saves the trace before closing its BrowserContext. A trace covers the session's main page and captured popups; different sessions produce different archives. Explicit tracing opens Trace Viewer by default for local debugging, while open: false is appropriate in CI. step/3 remains portable: it adds nested, source-linked trace groups when tracing is active and simply runs the callback on Phoenix or an untraced Playwright session.

Save an explicit PNG while retaining the pipeline with:

session
|> Playwright.screenshot("tmp/screenshots/polyjuice.png", full_page: true)
|> expect(visible(by_text("Potion ready")))

The configured Playwright console logger reports browser console messages and uncaught page errors without turning them into assertions. Separately, artifact_dir enables best-effort HTML, screenshot, and formatted-error files when a public browser operation fails. Diagnostic capture never replaces the original operation error.

Downloads, popups, navigation metadata, dialogs, and network events require a listener to be installed before the triggering action. Use the pipeable wait_for(Event.*(...)) APIs described in Advanced events and pages.

Native escape hatch

Use unwrap/2 for an uncommon driver-native operation that has no first-class Fluffy API. It returns the reconciled session, so the pipeline can continue, but the callback value is intentionally driver-specific:

session
|> unwrap(fn %Phoenix.LiveViewTest.View{} = view ->
  Phoenix.LiveViewTest.render_hook(view, "open-chamber", %{"phrase" => "open"})
end)
|> expect(visible(by_text("Chamber opened")))

The callback receives the current %Plug.Conn{} on a Static page, a %Phoenix.LiveViewTest.View{} on a LiveView page, or a %Fluffy.Playwright.Handle{} on a Playwright page.

A Static callback must return its updated Plug.Conn because connections are immutable. LiveView and Playwright callback results are ignored: Fluffy retains and reconciles the original View or Handle. Exceptions, throws, and exits pass through unchanged. Match PlaywrightEx {:error, reason} results inside the callback when failure should stop the test.

The Playwright handle exposes only context_id, page_id, frame_id, connection, and timeout. Operations that change owned lifecycle or require a listener before an action must use Fluffy's first-class APIs. Pre-arm navigation, pages, downloads, dialogs, requests, and responses with wait_for(Event.*(...)); manage named pages with switch_page and close_page. Closing a tracked page/context or creating an untracked page through unwrap/2 is unsupported.

Native callbacks do not promise portability between drivers. If an operation is repeated often—or Fluffy must own its timing, cleanup, or result—it is a good candidate for a small first-class API.

One backend per scenario

Choose the backend at session startup and keep the rest of the test focused on the user journey. Use Phoenix unless the behavior under test depends on a real browser. In that case, run the scenario with Playwright—not once with each.

Fluffy's own conformance corpus is parameterized across drivers because the library must prove its shared semantics. That machinery is deliberately not a consumer testing pattern.

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