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 embed simple tests for process success/failure and for stderr/stdout inside a 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::{path::PathBuf, process::Command};

use lang_tester::LangTester;
use tempdir::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("rust_lang_tester").unwrap();
    LangTester::new()
        .test_dir("examples/rust_lang_tester/lang_tests")
        // Only use files named `*.rs` as tests.
        .test_file_filter(|p| p.extension().unwrap().to_str().unwrap() == "rs")
        // Extract the first sequence of commented line(s) as the test.
        .test_extract(|s| {
            Some(
                s.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[2..])
                    .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 tests, running two commands against them: Compiler (i.e. rustc); and Run-time (the compiled binary).

Users can then write files with tests and their inputs such as the following:

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

Tests use a two-level indentation syntax: the outer most level of indentation defines a command name (multiple command names can be specified, as in the above); each command name can then define tests for one or more of status: <success|failure>, stderr: [<string>], stdout: [<string>].

In essence, each keyword under a command name is a test for that command. The above file contains 4 tests: 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 and produce Hello world on stdout.

Lines not mentioned are not tested: for example, the above file does not state whether the Compilers stdout should have content or not (but note that the line stdout: on its own would state that the Compiler should have no content at all). stderr/stdout tests can use ... as a simple wildcard: if a line consists solely of ..., it means "match zero or more lines"; if a line begins with ..., it means "match the remainder of the line only"; if a line ends with ..., it means "match the start of the line only". A line may start and end with .... stderr/stdout matches ignore leading/trailing whitespace and newlines, but are case sensitive.

lang_tester's output is deliberately similar to Rust's normal testing output. Running the example rust_lang_tester in this crate produces the following output:

$ cargo run --example=rust_lang_tester
   Compiling lang_tester v0.1.0 (/home/ltratt/scratch/softdev/lang_tester)
    Finished dev [unoptimized + debuginfo] target(s) in 3.41s
     Running `target/debug/examples/rust_lang_tester`

running 3 tests
test lang_tests::no_main ... ok
test lang_tests::unknown_var ... ok
test lang_tests::unused_var ... ok

test result: ok. 3 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out

lang_tester 0.1.0

lang_tester