Usage

Start each test with the Phoenix (:phoenix) or Playwright (:playwright) backend. 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 and locators; use Fluffy.Assert imports the assertion vocabulary:

defmodule MyAppWeb.CreatureTest do
  use ExUnit.Case, async: true
  use Fluffy.Assert

  import Fluffy
  import Fluffy.Locator

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

  test "puts Fluffy to sleep" do
    start_session(:phoenix)
    |> visit("/creatures/fluffy")
    |> fill(by_label("Keeper"), "Rubeus Hagrid")
    |> click(by_role(:button, name: "Play flute"))
    |> assert(visible(by_text("Asleep")))
    |> assert(page_url("/creatures/fluffy"))
  end
end

Actions and assertions return 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 examples describe an illustrative Hogwarts application; routes, controls, and event handlers must exist in the application under test. Later snippets assume the same imports and an initialized session. Upload examples also require the named fixture files.

The first 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. Choose the backend when starting the session:

test "updates the preview rendered by a JavaScript hook" do
  start_session(:playwright)
  |> visit("/creatures/new")
  |> fill(by_label("Name"), "Basilisk")
  |> assert(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.

See the capability matrix for backend differences.

Shared test case

Put shared imports and session setup in an application-owned FluffyCase. Keep your ordinary ConnCase for fixtures, routes, and sandbox setup, then start the Fluffy session after it:

# test/support/fluffy_case.ex
defmodule MyAppWeb.FluffyCase do
  use ExUnit.CaseTemplate

  using do
    quote do
      use MyAppWeb.ConnCase
      use Fluffy.Assert

      import Fluffy
      import Fluffy.Locator

      alias Fluffy.Event

      setup context do
        :ok = Fluffy.Test.setup(context)
        %{session: start_session(Map.get(context, :backend, :phoenix))}
      end
    end
  end
end

Tests receive session in their context and default to Phoenix. Use @moduletag backend: :playwright for an entire module, @describetag for a describe block, or @tag for one test—without a separate browser test module:

defmodule MyAppWeb.PotionTest do
  use MyAppWeb.FluffyCase, async: true

  test "lists the available potions", %{session: session} do
    session
    |> visit("/potions")
    |> assert(visible(by_text("Polyjuice Potion")))
  end

  @tag backend: :playwright
  test "brews a potion through a JavaScript hook", %{session: session} do
    session
    |> visit("/potions")
    |> click(by_role(:button, name: "Brew potion"))
    |> assert(visible(by_text("Potion brewed")))
  end
end

Locators

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

1. Use a label for a form control.
2. Use a role and accessible name for an interactive element.
3. Use text for rendered content, with a visibility assertion when needed.
4. Use a test ID when user-facing names are ambiguous.
5. Use CSS for structure that has no user-facing identity.

session
|> fill(by_label("Name"), "Basilisk")
|> click(by_role(:button, name: "Register"))
|> assert(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 assert(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"), %{label: "Asleep"})
|> click(by_role(:button, name: "Save creature"))
|> assert(enabled(by_role(:button, name: "Save creature")))
|> assert(disabled(by_label("Species")))
|> assert(value(by_label("Keeper"), "Rubeus Hagrid"))
|> assert(editable(by_label("Keeper")))
|> assert(checked(by_label("Flute ready")))
|> assert(visible(by_text("Creature saved")))

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

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

Static and LiveView raise Fluffy.CapabilityError for indeterminate state.

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.

Actionability checks and waiting

Playwright already checks each action's prerequisites and waits automatically for the target to be ready. As elsewhere in Fluffy, Playwright is the model we follow, with the Phoenix-specific limits described below. Usually you can act directly and assert the result, without first asserting that the target is ready:

session
|> fill(by_label("Potion name"), "Polyjuice Potion")
|> click(by_role(:button, name: "Save potion"))
|> assert(page_url(path: "/potions"))

The Phoenix backend checks HTML structure and control state. Each action requires exactly one matching target, with these additional checks:

For click, fill, check / uncheck, and select_option, LiveView also retries missing targets until the action deadline. Ambiguous locators and invalid control types fail immediately. Static checks immediately without waiting for later changes. A checkbox already in the requested state needs no mutation; unchecking a checked radio is invalid.

These are action-specific rules, not a blanket visibility requirement. Phoenix fill does not check visibility, and set_input_files intentionally accepts hidden or disabled file inputs. Locator matching may itself exclude hidden elements; see Visibility and DOM presence.

Phoenix does not compute CSS layout or detect overlapping elements. Playwright uses the browser's action-specific checks: for example, fill waits for rendered visibility, enablement, and editability, while click also waits for stability and the target to receive pointer events.

Keep separate assertions when the state itself is the behavior under test, such as a button becoming enabled after a required field is filled. assert(enabled(locator)) does not imply visibility, and neither does refute(disabled(locator)); the latter is the same negation as assert(not_(disabled(locator))) with not_/1 imported from Fluffy.Expect.

Form submission and keyboard actions

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.

LiveView supports declarative Enter, Space, and Tab handlers. Use Playwright for more complex keyboard behavior; see LiveView timing and keyboard events.

Assertions

The examples use use Fluffy.Assert, which imports assert, refute, and all assertion constructors. Place it after your ExUnit case module to preserve ordinary ExUnit assertions without import clashes. See Assertion styles for the equivalent expect vocabulary, constructor names, options, and negation semantics.

Visibility and DOM presence

Even the :phoenix backend checks structural visibility, rather than just DOM presence. Its Static and LiveView drivers treat a matched element with a hidden attribute or aria-hidden="true" as invisible. This differs from PhoenixTest's assert_has and refute_has, which check for matching DOM elements rather than their visibility.

Phoenix does not compute CSS or browser layout: a CSS class or inline display: none alone does not make an element structurally invisible. Use :playwright to test rendered visibility. Its browser visibility rules also differ from structural checks: aria-hidden="true" alone does not visually hide an element.

Choose the assertion that expresses the intended behavior:

# Require a visible element.
session |> assert(visible(by_css("#notice")))

# Allow the element to be absent or invisible.
session |> refute(visible(by_css("#notice")))

# Require DOM absence, including hidden elements.
session |> assert(count(by_css("#notice"), 0))

To require an element to remain in the DOM but be invisible, assert count(by_css("#notice"), 1) before refuting its visibility. Use a CSS locator for these presence checks; role locators can exclude structurally hidden elements before the assertion runs.

Page assertions

Page assertion constructors use a page_ prefix and target the active page:

session
|> assert(page_title("Chamber of Secrets"))
|> assert(page_title(~r/^Chamber/))
|> refute(page_title("Chamber sealed"))

Title assertions normalize whitespace. LiveView and Playwright retry until the title matches; Static checks immediately. LiveView also observes later @page_title updates.

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

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

Exact URL strings include the query and fragment; relative strings resolve against the session base URL. Structured matching can select :path, :query, and :fragment; omitted components are ignored. A function receives a %URI{}:

session |> assert(page_url(fn uri -> uri.path == "/potions" and uri.fragment == "ready" end))

Predicates work with both backends and with negated assertions. Keep them quick and nonblocking.

Structured queries decode like URLSearchParams: distinct parameter-name order is ignored, and repeated values retain their order and duplicates. Exact query mode rejects unrelated names; query_mode: :subset allows them while requiring all values for each requested name.

Reloading

Use reload/1 to reload the active document:

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

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\nPolyjuice Potion,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/3; see Advanced events and pages.

Browser diagnostics

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

alias Fluffy.Playwright

start_session(:playwright)
|> Playwright.trace(open: false)
|> visit("/potions/polyjuice")
|> step("Brew Polyjuice Potion", fn session ->
  session
  |> fill(by_label("Boomslang skin"), "3")
  |> 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)
|> assert(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. See Playwright setup for artifact, trace, and logger configuration.

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.

Browser-only evaluation

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

alias Fluffy.Playwright

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 because Phoenix does not execute client code.

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)
|> assert(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.