Writing Tests

Setup

Import the fixture:

typescript

import { describe, test, expect } from "vitest"
import { createTestTerminal } from "@termless/test"

createTestTerminal() wraps createTerminal() with the xterm.js backend and registers cleanup in afterEach -- no manual close() needed. Matchers are auto-registered when importing from "@termless/test".

For named backends (async -- handles WASM/native initialization):

typescript

import { createTestTerminalByName } from "@termless/test"

test("works on ghostty", async () => {
  const term = await createTestTerminalByName({ backendName: "ghostty" })
  term.feed("Hello")
  expect(term.screen).toContainText("Hello")
})

You can also pass a factory-created backend directly:

typescript

import { createGhosttyBackend, initGhostty } from "@termless/ghostty"

const ghostty = await initGhostty()
const term = createTestTerminal({ backend: createGhosttyBackend(undefined, ghostty) })

Deprecated aliases

createTerminalFixture and createTerminalFixtureAsync still work as deprecated aliases for createTestTerminal and createTestTerminalByName respectively.

Composable API

The key design principle: separate where to look from what to assert.

typescript

// WHERE: region selectors
term.screen // visible rows x cols area
term.scrollback // history above screen
term.buffer // everything (scrollback + screen)
term.viewport // current scroll position view
term.row(n) // screen row (negative from bottom)
term.cell(r, c) // single cell
term.range(r1, c1, r2, c2) // rectangular region
term.firstRow() // convenience: first screen row
term.lastRow() // convenience: last screen row

// WHAT: matchers
expect(term.screen).toContainText("Hello") // text matcher on region
expect(term.cell(0, 0)).toBeBold() // style matcher on cell
expect(term).toHaveCursorAt(5, 0) // terminal matcher

Matchers Reference

Text Matchers (on RegionView / RowView)

typescript

// Contains text anywhere in the region
expect(term.screen).toContainText("Hello")

// Exact text match (trimmed)
expect(term.row(0)).toHaveText("Title")

// Line-by-line match (trailing whitespace trimmed)
expect(term.screen).toMatchLines(["Line 1", "Line 2", "Line 3"])

Cell Style Matchers (on CellView)

typescript

// Colors — accepts "#rrggbb" string or { r, g, b } object
expect(term.cell(0, 0)).toHaveFg("#ff0000")
expect(term.cell(0, 0)).toHaveBg({ r: 0, g: 255, b: 0 })

// Text attributes
expect(term.cell(0, 0)).toBeBold()
expect(term.cell(0, 0)).toBeItalic()
expect(term.cell(0, 0)).toBeFaint()
expect(term.cell(0, 0)).toBeStrikethrough()
expect(term.cell(0, 0)).toBeInverse()
expect(term.cell(0, 0)).toBeWide() // Double-width character

// Underline -- optional style: "single" | "double" | "curly" | "dotted" | "dashed"
expect(term.cell(0, 0)).toHaveUnderline() // Any underline
expect(term.cell(0, 0)).toHaveUnderline("curly") // Specific style

Cursor Matchers

typescript

// Position (x, y)
expect(term).toHaveCursorAt(5, 0)

// Visibility
expect(term).toHaveCursorVisible()
expect(term).toHaveCursorHidden()

// Style: "block" | "underline" | "beam"
expect(term).toHaveCursorStyle("beam")

Terminal Mode Matchers

typescript

// Generic mode check (replaces toBeInAltScreen, toBeInBracketedPaste, toHaveMode)
expect(term).toBeInMode("altScreen")
expect(term).toBeInMode("bracketedPaste")
expect(term).toBeInMode("mouseTracking")
expect(term).toBeInMode("applicationCursor")

Available modes: altScreen, cursorVisible, bracketedPaste, applicationCursor, applicationKeypad, autoWrap, mouseTracking, focusTracking, originMode, insertMode, reverseVideo. See terminfo.dev for which terminals support which features.

Title Matcher

typescript

// OSC 2 title
expect(term).toHaveTitle("My App - untitled")

Scrollback Matchers

typescript

// Total lines in scrollback buffer
expect(term).toHaveScrollbackLines(100)

// Viewport at bottom (no scroll offset)
expect(term).toBeAtBottomOfScrollback()

Snapshot Matcher

typescript

// Vitest snapshot of terminal state
expect(term).toMatchTerminalSnapshot()

Negation

All matchers support .not:

typescript

expect(term.screen).not.toContainText("error")
expect(term.cell(0, 5)).not.toBeBold()
expect(term).not.toBeInMode("altScreen")

Snapshot Serializer

For readable terminal snapshots in .snap files:

typescript

import { expect } from "vitest"
import { terminalSerializer, terminalSnapshot } from "@termless/test"

expect.addSnapshotSerializer(terminalSerializer)

test("renders correctly", () => {
  const BOLD = (s: string) => `\x1b[1m${s}\x1b[0m`
  const term = createTestTerminal({ cols: 40, rows: 5 })
  term.feed(`${BOLD("Title")}\r\nContent`)

  expect(terminalSnapshot(term)).toMatchSnapshot()
})

Produces snapshots like:

# terminal 40x5 | cursor (7,1) visible block
--------------------------------------------------
 1|Title
 2|Content
 3|
 4|
 5|

With style annotations when cells have non-default attributes:

 1|Title  [0:bold] [1:bold] [2:bold] [3:bold] [4:bold]

Common Patterns

Testing ANSI output

typescript

const BOLD_RED = (s: string) => `\x1b[1;31m${s}\x1b[0m`

test("error message is red and bold", () => {
  const term = createTestTerminal()
  term.feed(`${BOLD_RED("Error:")} file not found`)

  expect(term.screen).toContainText("Error: file not found")
  expect(term.cell(0, 0)).toBeBold()
  expect(term.cell(0, 0)).toHaveFg("#800000") // ANSI red (palette index 1)
  expect(term.cell(0, 7)).not.toBeBold() // space after "Error:" is not bold
})

Testing cursor movement

typescript

test("cursor tracks input", () => {
  const term = createTestTerminal()
  term.feed("Hello")
  expect(term).toHaveCursorAt(5, 0)

  term.feed("\r\nWorld")
  expect(term).toHaveCursorAt(5, 1)
})

Testing interactive apps with PTY

typescript

test("app enters alt screen", async () => {
  const term = createTestTerminal({ cols: 80, rows: 24 })
  await term.spawn(["my-tui"])
  await term.waitForStable()

  expect(term).toBeInMode("altScreen")
  expect(term.screen).toContainText("Welcome")

  term.press("q")
  await term.waitForStable()
  expect(term).not.toBeInMode("altScreen")
})

Finding text positions

typescript

test("find specific text", () => {
  const term = createTestTerminal()
  term.feed("Line 0\r\nLine 1\r\nTarget here")

  const pos = term.find("Target")
  expect(pos).not.toBeNull()
  expect(pos!.row).toBe(2)
  expect(pos!.col).toBe(0)

  // Regex search for multiple matches
  const matches = term.findAll(/Line \d/g)
  expect(matches).toHaveLength(2)
})

Reading text from regions

typescript

test("read text from different regions", () => {
  const term = createTestTerminal({ cols: 80, rows: 5 })

  // Feed enough lines to create scrollback
  for (let i = 0; i < 10; i++) {
    term.feed(`Line ${i}\r\n`)
  }

  // Screen shows the last 5 rows
  const screenText = term.screen.getText()

  // Scrollback has the history
  const scrollbackText = term.scrollback.getText()

  // Buffer has everything
  const bufferText = term.buffer.getText()

  // Single row
  const rowText = term.row(0).getText()
})

Lazy Views & Auto-Retry

Region selectors (term.screen, term.scrollback, term.row(n), etc.) return lazy views -- they re-read from the terminal backend on every access. You never need to "refresh" a view; it always reflects the current terminal state.

This makes them work naturally with auto-retry matchers. When you await a matcher with a { timeout } option, vitest polls the lazy view repeatedly until the assertion passes or the timeout expires:

typescript

// The lazy view re-reads the terminal on each poll iteration
await expect(term.screen).toContainText("ready", { timeout: 10000 })

This replaces the deprecated waitFor() pattern:

typescript

// Deprecated -- no diff on failure, worse error messages
await term.waitFor("ready", 10000)

// Preferred -- integrates with vitest expect, shows diff on failure
await expect(term.screen).toContainText("ready", { timeout: 10000 })

You can combine lazy views with any matcher. The { timeout } option is supported by all text matchers (toContainText, toHaveText, toMatchLines) and terminal matchers (toHaveCursorAt, toBeInMode, etc.):

typescript

// Wait for cursor to reach a specific position
await expect(term).toHaveCursorAt(0, 5, { timeout: 5000 })

// Wait for a specific row to contain text
await expect(term.row(0)).toContainText("Title", { timeout: 5000 })

// Wait for alt screen mode
await expect(term).toBeInMode("altScreen", { timeout: 5000 })

Without { timeout }, matchers run synchronously -- they pass or fail immediately without polling. Use the synchronous form for in-memory tests where the terminal state is already set:

typescript

term.feed("\x1b[1mBold\x1b[0m")
expect(term.cell(0, 0)).toBeBold() // sync, no polling

Migration from Old API

Old	New
`await term.waitFor("x", 5000)`	`await expect(term.screen).toContainText("x", { timeout: 5000 })`
`expect(term).toContainText("x")`	`expect(term.screen).toContainText("x")`
`expect(term).toBeBoldAt(r, c)`	`expect(term.cell(r, c)).toBeBold()`
`expect(term).toHaveFgColor(r, c, color)`	`expect(term.cell(r, c)).toHaveFg(color)`
`expect(term).toBeInAltScreen()`	`expect(term).toBeInMode("altScreen")`
`expect(term).toMatchViewport(lines)`	`expect(term.screen).toMatchLines(lines)`
`term.getViewportText()`	`term.screen.getText()`
`term.getScrollbackText()`	`term.scrollback.getText()`
`term.getRowText(n)`	`term.row(n).getText()`

Writing Tests ​

Setup ​

Composable API ​

Matchers Reference ​

Text Matchers (on RegionView / RowView) ​

Cell Style Matchers (on CellView) ​

Cursor Matchers ​

Terminal Mode Matchers ​

Title Matcher ​

Scrollback Matchers ​

Snapshot Matcher ​

Negation ​

Snapshot Serializer ​

Common Patterns ​

Testing ANSI output ​

Testing cursor movement ​

Testing interactive apps with PTY ​

Finding text positions ​

Reading text from regions ​

Lazy Views & Auto-Retry ​

Migration from Old API ​

Writing Tests

Setup

Composable API

Matchers Reference

Text Matchers (on RegionView / RowView)

Cell Style Matchers (on CellView)

Cursor Matchers

Terminal Mode Matchers

Title Matcher

Scrollback Matchers

Snapshot Matcher

Negation

Snapshot Serializer

Common Patterns

Testing ANSI output

Testing cursor movement

Testing interactive apps with PTY

Finding text positions

Reading text from regions

Lazy Views & Auto-Retry

Migration from Old API