Crate term_transcript

Snapshot testing for CLI / REPL applications, in a fun way.

What it does

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.

Design decisions

• Static capturing. Capturing dynamic interaction with the terminal essentially requires writing / hacking together a new terminal, which looks like an overkill for the motivating use case (snapshot testing).

• (Primarily) static SVGs. Animated SVGs create visual noise and make simple things (e.g., copying text from an SVG) harder than they should be.

• Self-contained tests. Unlike generic snapshot files, Transcripts contain both user inputs and outputs. This allows using them as images with little additional explanation.

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 TermError::NonCsiSequence.
• Pseudo-terminal (PTY) APIs are not used in order to be more portable. This can change in the future releases.
• Since the terminal is not emulated, programs dependent on isatty checks can produce different output than if launched in an actual shell. One can argue that dependence on isatty is generally an anti-pattern.
• As a consequence of the last point, CLI tools frequently switch off output coloring if not writing to a terminal. For some tools, this can be amended by adding an arg to the command, such as --color=always.

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.
• 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.

Crate features

• svg. Exposes the eponymous module that allows rendering Transcripts into the SVG format.
• test. Exposes the eponymous module that allows parsing Transcripts from SVG files and testing them.
• pretty_assertions. Uses the eponymous crate when testing SVG files. Only really makes sense together with the test feature.

svg, test and pretty_assertions features are on by default.

Examples

Creating a terminal Transcript and rendering it to SVG.

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

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)?);

Loading a Transcript and testing it. See the test module for more examples.

use term_transcript::{test::TestConfig, ShellOptions, Transcript, UserInput};
use std::io;

fn read_svg_file() -> anyhow::Result<impl io::BufRead> {
    // snipped...
}

let reader = read_svg_file()?;
let transcript = Transcript::from_svg(reader)?;
TestConfig::new(ShellOptions::default()).test_transcript(&transcript);

Modules

svg	svg Provides the SVG template for rendering terminal output in a visual format.
test	test Snapshot testing tools for Transcripts.

Structs

Captured	Output captured from the terminal.
Interaction	One-time interaction with the terminal.
ShellOptions	Options for executing commands in the shell. Used in Transcript::from_inputs() and in TestConfig.
Transcript	Transcript of a user interacting with the terminal.
UserInput	User input during interaction with a terminal.

Enums

StdShell	Shell interpreter that brings additional functionality for ShellOptions.
TermError	Errors that can occur when processing terminal output.

Traits

TermOutput

Marker trait for supported types of terminal output.