Snapshot Testing for CLI / REPL Applications

Documentation:

This crate allows to:

Create transcripts of interacting with a terminal, capturing both the output text and ANSI-compatible color info.
Save these transcripts in the SVG format, so that they can be easily embedded as images into HTML / Markdown documents
Parse transcripts from SVG
Test that a parsed transcript actually corresponds to the terminal output (either as text or text + colors).

The primary use case is easy to create and maintain end-to-end tests for CLI / REPL apps. Such tests can be embedded into a readme file.

Usage

Add this to your Crate.toml:

[dependencies]
term-transcript = "0.2.0"

Example of usage:

use term_transcript::{
    svg::{Template, TemplateOptions}, ShellOptions, Transcript, UserInput,
};
use std::str;

let transcript = Transcript::from_inputs(
    &mut ShellOptions::default(),
    vec![UserInput::command(r#"echo "Hello world!""#)],
)?;
let mut writer = vec![];
// ^ Any `std::io::Write` implementation will do, such as a `File`.
Template::new(TemplateOptions::default()).render(&transcript, &mut writer)?;
println!("{}", str::from_utf8(&writer)?);
Ok::<_, anyhow::Error>(())

See more examples in the crate docs.

Snapshot examples

Here's an SVG snapshot of the rainbow example produced by this crate:

Snapshot of rainbow example

Here's a snapshot of the same example with the scrolling animation and window frame:

Animated snapshot of rainbow example

Limitations

Terminal coloring only works with ANSI escape codes. (Since ANSI escape codes are supported even on Windows nowadays, this shouldn't be a significant problem.)
ANSI escape sequences other than SGR ones are either dropped (in case of CSI sequences), or lead to an error.
By default, the crate exposes APIs to perform capture via OS pipes. Since the terminal is not emulated in this case, programs dependent on isatty checks or getting term size can produce different output than if launched in an actual shell (no coloring, no line wrapping etc.).
It is possible to capture output from a pseudo-terminal (PTY) using the portable-pty crate feature. However, since most escape sequences are dropped, this is still not a good option to capture complex outputs (e.g., ones moving cursor).
PTY support for Windows is shaky. It requires a somewhat recent Windows version (Windows 10 from October 2018 or newer), and may work incorrectly even for the recent versions.

Alternatives / similar tools

insta is a generic snapshot testing library, which is amazing in general, but kind of too low-level for E2E CLI testing.
rexpect allows testing CLI / REPL applications by scripting interactions with them in tests. It works in Unix only.
trybuild snapshot-tests output of a particular program (the Rust compiler).
Tools like termtosvg and Asciinema allow recording terminal sessions and save them to SVG. The output of these tools is inherently dynamic (which, e.g., results in animated SVGs). This crate intentionally chooses a simpler static format, which makes snapshot testing easier.

License

Licensed under either of Apache License, Version 2.0 or MIT license at your option.