Overview

Biloba: the mental model

Biloba is a browser-testing framework for Go, built on chromedp, for Ginkgo and Gomega. You don't . import it — drive everything through a *biloba.Biloba value (conventionally b). Canonical docs: https://onsi.github.io/biloba/ — pin to the version you go get'd (the API may shift pre-1.0).

The three principles — and what they mean for your specs

1. Performance via parallelization. One shared Chrome process drives one isolated root tab (b) per Ginkgo parallel process, reused between specs via b.Prepare().

• Run with ginkgo -p. Specs must be independent; Biloba's per-tab isolation makes that cheap.
• b is special: never closed, reused spec-to-spec. b.NewTab() tabs and spawned tabs are closed by Prepare(). → setup

2. Stability via pragmatism. Biloba prefers a good-enough simulation run atomically in the browser over a realistic emulation across async round-trips. A click is element.click() after synchronous visibility/enabled checks — no scroll-into-view, no centroid, no occlusion test. This fast track is the default b. Consequences to internalize:

• Visibility = non-zero offsetWidth/offsetHeight. The fast track won't catch an element hidden behind another or off-screen. Use b.HaveComputedStyle for explicit style assertions, or b.BeClickable() to assert topmost-at-its-center.
• b.SetValue sets the value and fires input/change — it does not type. Apps wired to real key events (search-as-you-type, rich text, hotkeys) need b.Type.
• b.Hover fires pointer/mouse events but does not activate CSS :hover.
• There are two interaction tracks. For the handful of specs that need real clicks through occlusion, scroll-into-view, CSS :hover, or drags, opt into b.Realistic() — a view of the same tab routed through real Chrome DevTools Protocol input. Per-spec opt-in (it costs round-trips and can reintroduce timing flake). → realistic-mode

3. Conciseness via Ginkgo and Gomega.

• Most methods don't return errors — errors become Ginkgo test failures for you.
• Appearance is assertable too. Eventually(sel).Should(b.HaveScreenshot("name")) compares the element (or the whole tab) against a committed baseline PNG, re-capturing on every poll attempt so the comparison waits out fonts and reflow. A missing baseline fails loudly rather than being written and passed. → visual-assertions
• Biloba polls by default. A fully-applied call (b.Click("#go"), b.GetProperty(sel, "href")) polls until the element is ready, acts/reads once, then stops. The under-applied form returns a Gomega matcher you wrap in Eventually/Consistently. This dual API is the core pattern — learn it in write-tests. (b.Immediate() opts back into act-once/fail-fast; rarely needed.)
• console.log streams to the GinkgoWriter; a failing console.assert fails the spec.

The one habit that keeps suites non-flaky

Never assert on a value you read exactly once. A browser is a pile of async settles (a WS frame, a layout pass, an rAF-injected node, an optimistic→server reconciliation), and any single read can land before the thing you care about settles. Biloba's poll-by-default actions and getters handle this — the residual flake sources are the few things that don't poll. Four reflexes:

• b.Run reads don't poll — wrap them. b.Run(expr, &x); Expect(x) is a single-shot read (Run stays fail-fast on purpose — a thrown JS error is usually a real bug). Write Eventually(b.Run).WithArguments(expr).Should(matcher) instead; numbers decode to float64, so use BeNumerically.
• Don't hand-roll geometry in b.Run either. Layout/getBoundingClientRect/computed-style reads settle after an element exists, so they must be polled even once it's there — and Biloba has layout-aware natives for nearly all of them (b.GetBoundingBox/GetScrollOffset/GetOffsetTopWithin + Have* matchers, the pairwise b.BeAbove/Encloses/Overlaps, b.BeInViewport(), b.BePrecededBy/BeFollowedBy, b.GetComputedStyle). → api
• Don't reach for b.Immediate(). The default already polls; reaching for it reintroduces the classic "raced a frame, failed downstream" flake. The few methods that genuinely can't poll (SendKeysToWindowImmediately, the *Immediately plural verbs) carry the smell in their names — gate them by hand. → flaky-specs
• Don't assert with a matcher and then re-read the value with a getter — two reads of a page that may have changed in between. Every value-reading matcher takes .Capture(&x): Eventually(sel).Should(b.HaveAttribute("data-id", Not(BeEmpty())).Capture(&id)) hands you the value from the read that actually satisfied the assertion, decoded into your Go type. → write-tests

If your app renders optimistically, both obvious signals lie. The DOM shows the pre-confirmation state (the click handler wrote it synchronously), so Eventually on it just re-reads the optimistic copy; a Go-side HTTP read bypasses the browser's event loop and proves only that the server persisted something. Barrier on app state — b.GetJSValue("window.__storeLog", &log) polls a path the app writes, which can only become true if the renderer applied the response — and force the arrival order with b.HoldResponse(url) instead of hoping to hit a 1%-natural race. (GetJSValue gates on definedness, so it only barriers on a path the app creates lazily, in the handler you're waiting for; against an eagerly-created log poll the predicate: Eventually(expr).Should(b.EvaluateTo(...)).) → flaky-specs

When a spec is flaky, order-dependent, or only fails under -p/CI, go straight to flaky-specs. To find out how often specs fail, or to confirm that a fix worked, run the suite many times and read the reports → flake-hunt.

Selectors are first-class — three pathways

Every action/matcher takes:

• a CSS string — the default; target stable #id/[data-testid] hooks, not styling classes. >>> pierces open shadow roots / same-origin iframes.
• a semantic Locator — describes an element as a user perceives it (b.ByRole("button").WithName("Save"), b.ByText, b.ByLabel, b.ByTestID). Reach for these to assert a11y or when the visible label is the natural identifier. They compose (.ContainingText/.Containing/.And/.Or/.Within/.Nth, each accepting any selector) and pierce open shadow roots automatically. b.ByCSS(sel) takes raw CSS into that algebra (b.ByCSS(".story").Nth(1) for the 2nd match, instead of :nth-of-type).
• an XPath — the rare power tool for axis/ordinal queries.

→ write-tests, xpath

The escape hatch

Biloba deliberately does not hide chromedp. Every tab exposes b.Context:

chromedp.Run(b.Context, chromedp.ActionFunc(func(ctx context.Context) error {
    return emulation.SetGeolocationOverride().WithLatitude(48.8584).WithLongitude(2.2945).Do(ctx)
}))

Use it for geolocation, cross-origin frames, or any CDP feature without a native wrapper. (For real :hover/occlusion/scroll, prefer b.Realistic().)

Where to go next

Sibling skills are named here without a prefix; invoke one with the same plugin prefix you loaded this skill under.