Warp TUI Unit Testing

tui-testing

How to write and run unit tests for Warp's headless TUI front-end (crates/warp_tui and the element library at crates/warpui_core/src/elements/tui). This complements rust-unit-tests (general Rust test conventions) and parallels gui-integration-test for the TUI.

TUI tests are plain, fast unit tests: they render an element tree to a fixed cell grid and assert on the resulting text lines. They do not use the GUI real-display / integration / computer-use framework (that's gui-integration-test / gui-integration-test-video, which are GUI-only).

Two test locations, two harnesses

TUI tests live in two crates, and which render helper you use depends on where the test is:

Element-library tests (in warpui_core)

Tests for the shared cell-grid elements live in crates/warpui_core/src/elements/tui/*_tests.rs and use the crate-internal test_support helpers from crates/warpui_core/src/elements/tui/mod.rs:

• test_support::render_to_lines(element: &dyn TuiElement, size: TuiSize) -> Vec<String> — one-call harness: builds area = TuiRect::new(0, 0, size.width, size.height) and TuiBuffer::empty(area), calls element.render(area, &mut buffer, ctx) inside a paint context, and returns buffer.to_lines(). It only calls render, not layout — fine for a leaf like TuiText, but composite elements (e.g. TuiFlex) populate child sizes during layout, so lay the element out first (see the layout_at helper in flex_tests.rs) or it renders empty/stale.
• test_support::with_paint_context(|ctx| ...) — runs a closure with a TuiPaintContext over a fresh, empty view map. Use it when you need the TuiBuffer afterward to assert on individual Cells.

These helpers are pub(crate) to warpui_core, so they are only callable from that crate's own tests. Simplest leaf assertion (see text_tests.rs, flex_tests.rs):

assert_eq!(
    render_to_lines(&TuiText::new("hello"), TuiSize::new(10, 1)),
    vec!["hello     "],
);

View/screen tests (in warp_tui)

warp_tui tests (crates/warp_tui/src/*_tests.rs) can NOT use test_support — render directly instead, under an App::test read/update so an AppContext is available. layout must run before render so child sizes are populated. This local helper mirrors render_element in transcript_view_tests.rs and render_lines in editor_element_tests.rs:

fn render_lines(app_ctx: &AppContext, mut element: impl TuiElement, w: u16, h: u16) -> Vec<String> {
    let mut rendered_views = EntityIdMap::default();
    let mut lctx = TuiLayoutContext { rendered_views: &mut rendered_views };
    let size = element.layout(TuiConstraint::loose(TuiSize::new(w, h)), &mut lctx, app_ctx);
    let area = TuiRect::new(0, 0, size.width, size.height);
    let mut buffer = TuiBuffer::empty(area);
    let mut paint_ctx = TuiPaintContext::new(&mut rendered_views);
    element.render(area, &mut buffer, &mut paint_ctx);
    buffer.to_lines()
}

Views that resolve theme styles need an Appearance singleton (ctx.add_singleton_model(|_| Appearance::mock())). To exercise a whole view through the real draw path, drive the presenter: TuiPresenter::new(), presenter.invalidate(&invalidation, ctx, window_id), then presenter.present(ctx, &view, area) and assert on frame.buffer.to_lines() (see transcript_view_tests.rs).

Asserting on styles, cursor, and events

• Styles/colors: paint into a buffer yourself and index cells. to_lines() only carries glyphs, so style assertions read Cell fields:

let mut buffer = TuiBuffer::empty(TuiRect::new(0, 0, 1, 1));
with_paint_context(|ctx| text.render(TuiRect::new(0, 0, 1, 1), &mut buffer, ctx));
let cell = &buffer[(0, 0)];
assert_eq!(cell.symbol(), "a");
assert_eq!(cell.fg, Color::Red);
assert!(cell.modifier.contains(Modifier::BOLD));

(with_paint_context is the warpui_core-only helper; in a warp_tui test construct the paint context directly with TuiPaintContext::new(&mut rendered_views) as in the render_lines helper above.)

• Cursor: call element.cursor_position(area, ctx) and assert on the returned Option<(u16, u16)>.
• Events: build a TuiEvent (e.g. TuiEvent::KeyDown { keystroke, chars, details, is_composing } or TuiEvent::ScrollWheel { .. }), then call element.dispatch_event(&event, area, &mut event_ctx, &mut layout_ctx, app_ctx) and assert on the returned bool and on the re-rendered lines/cursor. Layout must run first. See render_element / dispatch_event / dispatch_scroll helpers in crates/warp_tui/src/transcript_view_tests.rs.

Keep test areas at a stable, small width/height so golden line vectors stay readable and deterministic; trailing padding is spaces (e.g. "hello ").