lang_tester

This crate provides a simple language testing framework designed to help when you are testing things like compilers and virtual machines. It allows users to express simple tests for process success/failure and for stderr/stdout, including embedding those tests directly in the source file. It is loosely based on the compiletest_rs crate, but is much simpler (and hence sometimes less powerful), and designed to be used for testing non-Rust languages too.

For example, a Rust language tester, loosely in the spirit of compiletest_rs, looks as follows:

use std::{env, fs::read_to_string, path::PathBuf, process::Command};

use lang_tester::LangTester;
use tempfile::TempDir;

fn main() {
    // We use rustc to compile files into a binary: we store those binary files
    // into `tempdir`. This may not be necessary for other languages.
    let tempdir = TempDir::new().unwrap();
    LangTester::new()
        .test_dir("examples/rust_lang_tester/lang_tests")
        // Only use files named `*.rs` as test files.
        .test_path_filter(|p| p.extension().and_then(|x| x.to_str()) == Some("rs"))
        // Treat lines beginning with "#" inside a test as comments.
        .comment_prefix("#")
        // Extract the first sequence of commented line(s) as the tests.
        .test_extract(|p| {
            read_to_string(p)
                .unwrap()
                .lines()
                // Skip non-commented lines at the start of the file.
                .skip_while(|l| !l.starts_with("//"))
                // Extract consecutive commented lines.
                .take_while(|l| l.starts_with("//"))
                .map(|l| &l[COMMENT_PREFIX.len()..])
                .collect::<Vec<_>>()
                .join("\n")
        })
        // We have two test commands:
        //   * `Compiler`: runs rustc.
        //   * `Run-time`: if rustc does not error, and the `Compiler` tests
        //     succeed, then the output binary is run.
        .test_cmds(move |p| {
            // Test command 1: Compile `x.rs` into `tempdir/x`.
            let mut exe = PathBuf::new();
            exe.push(&tempdir);
            exe.push(p.file_stem().unwrap());
            let mut compiler = Command::new("rustc");
            compiler.args(&["-o", exe.to_str().unwrap(), p.to_str().unwrap()]);
            // Test command 2: run `tempdir/x`.
            let runtime = Command::new(exe);
            vec![("Compiler", compiler), ("Run-time", runtime)]
        })
        .run();
}

This defines a lang tester that uses all *.rs files in a given directory as test files, running two test commands against them: Compiler (i.e. rustc); and Run-time (the compiled binary).

Users can then write test files such as the following:

// Compiler:
//   stderr:
//     warning: unused variable: `x`
//       ...unused_var.rs:12:9
//       ...
//
// Run-time:
//   stdout: Hello world
fn main() {
    let x = 0;
    println!("Hello world");
}

The above file contains 4 meaningful tests, two specified by the user and two implied by defaults: the Compiler should succeed (e.g. return a 0 exit code when run on Unix), and its stderr output should warn about an unused variable on line 12; and the resulting binary should succeed produce Hello world on stdout.

Integration with Cargo.

Tests created with lang_tester can be used as part of an existing test suite and can be run with the cargo test command. For example, if the Rust source file that runs your lang tests is lang_tests/run.rs then add the following to your Cargo.toml:

[[test]]
name = "lang_tests"
path = "lang_tests/run.rs"
harness = false