testty

Rust-native TUI end-to-end testing framework. Drives a real TUI binary in a pseudo-terminal, captures location-aware terminal state with vt100, and provides a semantic assertion API for text, style, color, and region checks. Scenarios can also be compiled into VHS tapes for visual screenshot capture.

Installation

Add testty as a dev-dependency in the crate that contains your E2E tests:

[dev-dependencies]
testty = "0.8"
tempfile = "3"

Inside this workspace, keep using shared workspace dependencies instead:

# crates/my-app/Cargo.toml
[dev-dependencies]
testty = { workspace = true }
tempfile = { workspace = true }

Note: workspace = true requires matching entries in the root Cargo.toml under [workspace.dependencies].

Upgrading

The curated stable surface lives at testty::prelude and is locked down by the tests/public_api.rs tripwire test. Any breaking change to a prelude item or to the documented auxiliary items (testty::recipe, testty::snapshot::DEFAULT_UPDATE_ENV_VAR, SnapshotConfig::with_update_env_var, SnapshotConfig::with_update_mode, SnapshotConfig::is_update_mode) requires a deliberate update to that test and a testty major version bump.

When upgrading from earlier 0.x releases:

• Replace use testty::scenario::Scenario; / use testty::session::*; imports with use testty::prelude::*;.
• The artifact, calibration, and overlay modules have been removed. Use the proof pipeline backends and the snapshot testing helpers instead.
• testty::snapshot::is_update_mode() has been removed. Use SnapshotConfig::is_update_mode(&self) instead, which now resolves the per-config env var or the programmatic override set via SnapshotConfig::with_update_env_var / SnapshotConfig::with_update_mode.
• Snapshot baseline updates still default to TUI_TEST_UPDATE=1. Custom CI integrations can override the trigger via SnapshotConfig::with_update_env_var and read the default from testty::snapshot::DEFAULT_UPDATE_ENV_VAR.
• SnapshotConfig is now #[non_exhaustive]. Replace any struct-literal construction (SnapshotConfig { .. }) with SnapshotConfig::new(..) plus the with_* builder chain.
• SnapshotError and its struct-shaped variants (Mismatch, MissingBaseline, FrameMismatch) are now #[non_exhaustive]. match arms must include a fallback _ arm and any field destructuring must use the .. rest-pattern. The MissingBaseline variant also carries a new update_env_var field that surfaces the configured trigger in the error message.
• feature::GifStatus is now #[non_exhaustive] and gained Fresh { gif_path, hash } and Stale { gif_path, current, committed } variants used by the new FeatureDemo::gif_mode(GifMode::CheckOnly) freshness mode. CheckOnly is a read-only verification path: it never invokes VHS and never mutates the filesystem, so it works on read-only CI mounts and against missing output directories. Existing match arms must add a fallback _ arm and any field destructuring must use the .. rest-pattern. The companion helpers feature::compute_frame_hash and feature::hash_sidecar_path are now public so external tooling can reproduce the same hash that FeatureDemo writes to the on-disk sidecar.
• The feature-demo surface (FeatureDemo, FeatureMeta, FeatureResult, GifMode, GifStatus) is now re-exported from testty::prelude, so use testty::prelude::*; consumers can call FeatureDemo::new(..).gif_mode(..) without an explicit use testty::feature::..; import.

Quick start

Most users only need the curated [testty::prelude]:

use testty::prelude::*;

#[test]
fn startup_shows_welcome() {
    // Arrange
    let temp = tempfile::TempDir::new().unwrap();
    let builder = PtySessionBuilder::new("/path/to/my-binary")
        .size(80, 24)
        .env("MY_APP_ROOT", temp.path().to_string_lossy())
        .workdir(temp.path());

    let scenario = Scenario::new("startup")
        .wait_for_stable_frame(500, 5000)
        .capture();

    // Act
    let frame = scenario.run(builder).expect("scenario failed");

    // Assert
    testty::recipe::expect_instruction_visible(&frame, "Welcome");
}

Run the test:

cargo test -p my-app --test e2e

Core concepts

Scenario

A Scenario is an ordered sequence of Step actions that describe a user journey. Built with a fluent API, then executed in a PTY or compiled into a VHS tape.

use std::time::Duration;
use testty::scenario::Scenario;

let scenario = Scenario::new("tab_navigation")
    .wait_for_stable_frame(500, 5000)   // Wait for app to render
    .press_key("Tab")                    // Switch tab
    .wait_for_stable_frame(300, 3000)   // Wait for re-render
    .capture();                          // Snapshot the terminal

Steps

Each Step represents a single user action or wait condition:

| Step | Description | Example | |------|-------------|---------| | WriteText | Type text into the terminal | .write_text("hello world") | | PressKey | Send a named key press | .press_key("Enter") | | Sleep | Pause for a fixed duration | .sleep_ms(200) | | WaitForText | Poll until text appears | .wait_for_text("Ready", 5000) | | WaitForStableFrame | Wait for rendering to stabilize | .wait_for_stable_frame(500, 5000) | | Eventually | Poll a frame predicate until it succeeds | .eventually(timeout, poll, predicate) | | Capture | Snapshot the current terminal state | .capture() | | CaptureLabeled | Labeled snapshot for proof reports | .capture_labeled("init", "App launched") |

Predicate-driven waits with eventually

Step::eventually polls a closure against the live PTY frame on every tick and returns the moment the predicate returns Ok(()). On timeout, the executor surfaces the last AssertionFailure the predicate produced through PtySessionError::Assertion, so the structured failure context flows into the proof report instead of a generic timeout panic.

Use it whenever you would otherwise fight to pick a stable_ms/timeout_ms that is neither too long (wasted wall time) nor too short (flaky CI). It composes any MatchResult-returning predicate, so you can wait on assertion::match_* matchers, recipe checks, or your own frame inspection logic:

use std::time::Duration;
use testty::prelude::*;

let scenario = Scenario::new("counter_eventually")
    .write_text("+++")
    // Step::Sleep guesses how long the UI takes to repaint and risks
    // returning before the counter increments.
    .sleep_ms(200)
    // Step::WaitForText only checks for a literal substring and cannot
    // express richer predicates such as "selected tab is highlighted".
    .wait_for_text("Counter:", 5_000)
    // Step::eventually polls the predicate every 50ms and returns the
    // instant `Counter: 3` appears anywhere in the frame.
    .eventually(
        Duration::from_secs(5),
        Duration::from_millis(50),
        |frame| {
            assertion::match_text_in_region(
                frame,
                "Counter: 3",
                &Region::full(80, 24),
            )
        },
    )
    .capture();

Supported key names: Enter, Tab, Escape / Esc, Backspace, Up, Down, Left, Right, Home, End, Delete, PageUp, PageDown, Space, Ctrl+<letter> (e.g., Ctrl+C). Unknown keys are sent as raw bytes.

PtySession and PtySessionBuilder

PtySession spawns the binary in a real PTY using portable-pty. Configure it with PtySessionBuilder:

use testty::session::PtySessionBuilder;

let builder = PtySessionBuilder::new("/path/to/binary")
    .size(120, 40)                          // Terminal dimensions (default: 80x24)
    .args(["--help"])                       // Forward CLI args to the binary
    .env("DATABASE_URL", "sqlite::memory:") // Environment variables
    .env("LOG_LEVEL", "debug")
    .workdir("/tmp/test-workspace");        // Working directory

// Option 1: Use with a Scenario
let frame = scenario.run(builder).expect("failed");

// Option 2: Manual control
let mut session = builder.spawn().expect("spawn failed");
session.write_text("hello")?;
session.press_key("Enter")?;
let frame = session.wait_for_text("response", std::time::Duration::from_secs(5))?;

TerminalFrame

A TerminalFrame is a snapshot of the terminal state parsed through vt100. It provides structured access to text, colors, and styles:

use testty::frame::TerminalFrame;

// Create from raw ANSI bytes (done automatically by PtySession)
let frame = TerminalFrame::new(80, 24, b"\x1b[1mBold Title\x1b[0m\r\nBody text");

// Read text — wide-character continuation cells are skipped (the leading
// cell already supplies the full glyph), while real blank columns stay as
// spaces so column positions in the rendered terminal are preserved.
let all_text = frame.all_text();          // All visible text
let row_text = frame.row_text(0);         // Text from row 0
let region_text = frame.text_in_region(&region); // Text in a region

// Search for text (returns Vec<MatchedSpan>)
let matches = frame.find_text("Title");   // Find everywhere
let matches = frame.find_text_in_region("Title", &region); // Find in region

Region

A Region defines a rectangular area for scoped assertions:

use testty::region::Region;

// Named constructors
let header  = Region::top_row(80);           // First row, full width
let footer  = Region::footer(80, 24);        // Last row, full width
let full    = Region::full(80, 24);          // Entire terminal
let left    = Region::left_panel(80, 24);    // Left half
let right   = Region::right_panel(80, 24);   // Right half
let top_l   = Region::top_left(80, 24);      // Top-left quadrant
let top_r   = Region::top_right(80, 24);     // Top-right quadrant

// Percentage-based (col%, row%, width%, height%, cols, rows)
let upper = Region::percent(0, 0, 100, 60, 80, 24); // Top 60%

// Explicit coordinates
let custom = Region::new(10, 5, 30, 3);      // col=10, row=5, 30x3

MatchedSpan

When text is found in a frame, you get a MatchedSpan with position, color, and style metadata:

let matches = frame.find_text("Projects");
let span = &matches[0];

span.text;           // "Projects"
span.rect;           // Region { col, row, width, height }
span.foreground;     // Option<CellColor>
span.background;     // Option<CellColor>
span.style;          // CellStyle (bold, italic, underline, inverse)
span.is_bold();      // true if bold
span.is_highlighted(); // true if bold, inverse, or has background color
span.has_fg(&color); // true if foreground matches
span.has_bg(&color); // true if background matches

Assertion API

Low-level assertions (assertion module)

use testty::assertion;
use testty::frame::CellColor;
use testty::region::Region;

let region = Region::top_row(80);

// Text presence
assertion::assert_text_in_region(&frame, "Projects", &region);
assertion::assert_not_visible(&frame, "Error");
assertion::assert_match_count(&frame, "Tab", 2);

// Style checks
assertion::assert_span_is_highlighted(&frame, "Selected");
assertion::assert_span_is_not_highlighted(&frame, "Inactive");

// Color checks
assertion::assert_text_has_fg_color(&frame, "Error", &CellColor::new(128, 0, 0));
assertion::assert_text_has_bg_color(&frame, "Active", &CellColor::new(0, 0, 128));

All assert_* functions panic with detailed messages on failure, including the match position, actual colors/styles, and region contents.

Result-returning matchers (match_*)

Every assert_* has a match_* sibling that returns Result<(), Box<AssertionFailure>> (aliased as MatchResult) instead of panicking. The failure is boxed so the Ok path stays a single pointer-sized return and the Result enum stays small. Use the matcher form when you need to compose, retry, soft-batch, or surface failures into a proof report — for example, when polling the live PTY frame for a condition or when collecting multiple expectations against one capture.

use testty::assertion::{self, AssertionFailure, Expected, MatchResult};
use testty::region::Region;

let region = Region::top_row(80);

let result: MatchResult = assertion::match_text_in_region(&frame, "Projects", &region);
if let Err(failure) = result {
    // `failure.message` is the same byte-compatible string the panic adapter
    // would have produced, while `failure.expected`, `failure.region`, and
    // `failure.matched_spans` carry the structured context for renderers.
    match &failure.expected {
        Expected::TextInRegion { needle } => eprintln!("missing: {needle}"),
        _ => {}
    }
}

Adding the match_* siblings is a strictly additive change: all existing assert_* callers keep working without modification, so this evolution does not require a major version bump for downstream crates.

Soft-batched assertions (SoftAssertions)

SoftAssertions collects multiple match_* failures against one captured frame and panics once at scope end with every recorded message in record order, instead of failing fast on the first miss. Pass each MatchResult to check; passing results are dropped and failing ones are stored.

use testty::assertion::{self, SoftAssertions};
use testty::region::Region;

let region = Region::top_row(80);

{
    let mut soft = SoftAssertions::new();
    soft.check(assertion::match_text_in_region(&frame, "Projects", &region));
    soft.check(assertion::match_text_in_region(&frame, "Sessions", &region));
    soft.check(assertion::match_not_visible(&frame, "Error"));
    // Drop at the end of this block panics with one aggregated message
    // listing every failure that was recorded above.
}

Use SoftAssertions::into_failures to take ownership of the recorded failures before the accumulator goes out of scope; that path suppresses the end-of-scope panic so the caller can render the failures themselves.

To attach every recorded failure to the most recent ProofCapture::assertions entry on a ProofReport, construct the accumulator with SoftAssertions::with_report. The report must already hold at least one capture — call ProofReport::add_capture first, otherwise with_report panics at the bind site so misconfigurations surface immediately instead of silently dropping failures from the proof report.

use testty::assertion::{self, SoftAssertions};
use testty::proof::report::ProofReport;
use testty::region::Region;

let mut report = ProofReport::new("scenario");
report.add_capture("startup", "Startup snapshot", &frame);

let mut soft = SoftAssertions::with_report(&mut report);
soft.check(assertion::match_text_in_region(&frame, "Projects", &Region::top_row(80)));
soft.check(assertion::match_not_visible(&frame, "Error"));
// Each recorded failure also lands on the latest capture's assertions
// list so structured proof backends can render every failure together.
let _ = soft.into_failures();

Recipe helpers (recipe module)

High-level, composable helpers for common TUI patterns. Prefer these over raw assertions:

use testty::recipe;

// Tabs
recipe::expect_selected_tab(&frame, "Projects");     // In header, highlighted
recipe::expect_unselected_tab(&frame, "Sessions");    // In header, not highlighted

// Footer
recipe::expect_keybinding_hint(&frame, "Tab");        // Hint in footer row
recipe::expect_footer_action(&frame, "Quit");         // Action in footer row

// Content
recipe::expect_instruction_visible(&frame, "Press Enter to start");
recipe::expect_dialog_title(&frame, "Confirm Delete"); // Upper 60% of terminal
recipe::expect_status_message(&frame, "Saved");        // Anywhere in frame

// Absence
recipe::expect_not_visible(&frame, "Loading...");

Snapshot testing

The framework supports two snapshot modes: frame text (semantic) and visual screenshot (pixel-level via VHS).

Frame text snapshots

Compare the terminal text content against a committed baseline:

use testty::snapshot::{self, SnapshotConfig};

let config = SnapshotConfig::new(
    "tests/e2e_baselines",  // Committed baseline directory
    "tests/e2e_artifacts",  // Failure artifact output (gitignored)
);

snapshot::assert_frame_snapshot_matches(
    &config,
    "startup_projects_tab",  // Snapshot name
    &frame.all_text(),
).expect("frame snapshot should match");

Visual snapshots (VHS)

Compile a scenario into a VHS tape for pixel-level screenshot capture:

let tape = scenario.to_vhs_tape(
    &binary_path,
    Path::new("/tmp/screenshot.png"),
    &[("MY_ENV", "value")],
);

// Write tape to file
tape.write_to(Path::new("/tmp/test.tape"))?;

// Execute the tape (requires VHS installed)
tape.execute(Path::new("/tmp/test.tape"))?;

Updating baselines

Set TUI_TEST_UPDATE=1 to overwrite baselines with the current output:

TUI_TEST_UPDATE=1 cargo test -p my-app --test e2e

The variable name is configurable via SnapshotConfig::with_update_env_var; the default is exposed as testty::snapshot::DEFAULT_UPDATE_ENV_VAR.

For tests and other programmatic callers, SnapshotConfig::with_update_mode injects the update-mode decision directly. This bypasses the environment variable, which is the recommended way to drive update behavior from a test without mutating process-global env state through unsafe std::env::set_var calls:

let config = SnapshotConfig::new("tests/baselines", "tests/artifacts")
    .with_update_mode(true);

Snapshot config tuning

For visual snapshots, configure pixel-level comparison thresholds:

let config = SnapshotConfig::new("tests/baselines", "tests/artifacts")
    .with_thresholds(
        30.0,  // Per-pixel color distance threshold (Euclidean RGB)
        10.0,  // Maximum percentage of differing pixels allowed
    );

Proof pipeline

The proof pipeline captures labeled terminal states during scenario execution and renders them through swappable backends. Use capture_labeled() steps and run_with_proof() to collect a ProofReport:

use testty::scenario::Scenario;
use testty::session::PtySessionBuilder;
use testty::proof::frame_text::FrameTextBackend;
use testty::proof::strip::ScreenshotStripBackend;
use testty::proof::gif::GifBackend;
use testty::proof::html::HtmlBackend;

let scenario = Scenario::new("startup_proof")
    .wait_for_stable_frame(300, 5000)
    .capture_labeled("launched", "App reached stable state")
    .press_key("Tab")
    .wait_for_stable_frame(200, 3000)
    .capture_labeled("navigated", "Switched to second tab");

let builder = PtySessionBuilder::new("/path/to/binary").size(80, 24);
let (_frame, report) = scenario.run_with_proof(builder).expect("failed");

// Render through any backend:
report.save(&FrameTextBackend, Path::new("proof.txt")).unwrap();
report.save(&ScreenshotStripBackend, Path::new("proof.png")).unwrap();
report.save(&GifBackend::default(), Path::new("proof.gif")).unwrap();
report.save(&HtmlBackend, Path::new("proof.html")).unwrap();

Proof formats

| Format | Backend | Output | Use case | |--------|---------|--------|----------| | Frame text | FrameTextBackend | .txt | CI logs, quick inspection | | PNG strip | ScreenshotStripBackend | .png | Review comments, docs | | Animated GIF | GifBackend | .gif | PR descriptions, demos | | HTML report | HtmlBackend | .html | Detailed review with diffs and assertions |

Composable journeys

Journey provides reusable building blocks for declarative scenario authoring. Instead of repeating low-level step sequences, compose scenarios from pre-built journeys:

use testty::journey::Journey;
use testty::scenario::Scenario;

let startup = Journey::wait_for_startup(300, 5000);
let navigate = Journey::navigate_with_key("Tab", "Settings", 3000);
let input = Journey::type_and_confirm("search query");
let snapshot = Journey::capture_labeled("final", "End state");

let scenario = Scenario::new("settings_search")
    .compose(&startup)
    .compose(&navigate)
    .compose(&input)
    .compose(&snapshot);

Built-in journeys

| Journey | Steps | Description | |---------|-------|-------------| | wait_for_startup(stable_ms, timeout_ms) | 1 | Wait for app to render and stabilize | | navigate_with_key(key, expected, timeout) | 2 | Press key, wait for expected text | | type_and_confirm(text) | 2 | Type text and press Enter | | press_and_wait(key, ms) | 2 | Press key and sleep briefly | | capture_labeled(label, desc) | 1 | Capture with label for proofs |

Frame diffing

The diff engine computes cell-level differences between terminal frames and generates human-readable change summaries:

use testty::diff::FrameDiff;
use testty::frame::TerminalFrame;

let before = TerminalFrame::new(80, 24, b"Counter: 0");
let after = TerminalFrame::new(80, 24, b"Counter: 42");

let diff = FrameDiff::compute(&before, &after);
assert!(!diff.is_identical());

// Get changed regions with row/col spans
for region in diff.changed_regions() {
    println!("Row {}, cols {}..{}: {:?}",
        region.region.row, region.region.col,
        region.region.col + region.region.width,
        region.change_type);
}

// Human-readable summaries
for line in diff.summary() {
    println!("{line}");
}

Diffs are automatically computed between consecutive captures in a ProofReport and displayed in the HTML proof backend.

Module overview

| Module | Purpose | |--------|---------| | scenario | Fluent builder for composing test scenarios from steps | | step | Step enum: WriteText, PressKey, Sleep, WaitForText, WaitForStableFrame, Eventually, Capture, CaptureLabeled | | session | PTY executor: PtySession + PtySessionBuilder | | frame | Terminal state parser: TerminalFrame, CellColor, CellStyle | | region | Rectangular region definitions with named anchors | | locator | MatchedSpan with text, position, color, and style metadata | | assertion | Structured assertion functions with detailed failure messages | | recipe | High-level helpers for tabs, footer, dialogs, status messages | | snapshot | Baseline management: frame text and visual image comparison | | vhs | VHS tape compiler for visual screenshot capture | | proof | Proof pipeline: report collector, backend trait, and format implementations | | diff | Cell-level frame diffing with changed region detection | | journey | Composable journey building blocks for declarative test authoring | | feature | FeatureDemo builder: scenario execution with hash-cached VHS GIF generation | | prelude | Curated re-exports for the common testty workflow (use testty::prelude::*;) |

Full example

A complete E2E test exercising tab navigation:

use testty::prelude::*;
use testty::{recipe, snapshot};
use testty::snapshot::SnapshotConfig;

#[test]
fn tab_key_switches_tabs() {
    // Arrange
    let temp = tempfile::TempDir::new().unwrap();
    let builder = PtySessionBuilder::new(env!("CARGO_BIN_EXE_myapp"))
        .size(80, 24)
        .env("APP_ROOT", temp.path().to_string_lossy())
        .workdir(temp.path());

    let scenario = Scenario::new("tab_switch")
        .wait_for_stable_frame(500, 5000)
        .press_key("Tab")
        .wait_for_stable_frame(300, 3000)
        .capture();

    // Act
    let frame = scenario.run(builder).expect("scenario failed");

    // Assert
    recipe::expect_selected_tab(&frame, "Sessions");
    recipe::expect_unselected_tab(&frame, "Projects");

    // Optional: frame snapshot
    let config = SnapshotConfig::new("tests/e2e_baselines", "tests/e2e_artifacts");
    snapshot::assert_frame_snapshot_matches(&config, "tab_switch", &frame.all_text())
        .expect("frame snapshot should match");
}

Examples

Run the showcase examples to see the framework features in action:

# Full proof pipeline: captures → frame-text, PNG strip, GIF, HTML
cargo run --example proof_pipeline -p testty

# Frame diffing with changed region detection
cargo run --example frame_diffing -p testty

# Composable journeys and scenario building
cargo run --example journey_composition -p testty

Tips

• Use wait_for_stable_frame instead of sleep_ms when waiting for rendering. It adapts to actual render speed rather than hard-coding delays.
• Use recipe helpers over raw assertions. They encode common TUI layout patterns (header tabs, footer hints) so you don't rebuild locator logic.
• Set deterministic terminal size (e.g., 80x24) to keep frame snapshots stable across machines.
• Isolate state with tempfile::TempDir and environment variables so tests don't interfere with each other or the real app data.
• E2E tests run automatically with cargo test. Cargo builds the binary before running integration tests, so CARGO_BIN_EXE_* is always available.