Docker Test Helper

This is a small helper library to build and run Rust applications inside a Docker container. Its main use is to test applications that require specific file paths or permissions that would be inappropriate to perform locally on a development machine (e.g. chmod to root or enabling setuid).

Right now it is somewhat specific to my use-cases, but may be of use to others.

```rust

use docker_test::*;

[test]

fn help() { let container = setup("rsu", None).unwrap(); let out = container.exec(vec![container.deststr(), "--help"]).unwrap(); let stdout = String::fromutf8(out.stdout).unwrap(); assert!(out.status.success()); assert!(stdout.contains("Run commands as a user")); }

[test]

fn notroot() { let container = setup("rsu", None).unwrap(); let out = container.execas(TESTUSER, vec![container.deststr(), "/bin/ls"]).unwrap(); assert!(!out.status.success()); assert!(String::fromutf8(out.stderr).unwrap() .contains("Error: Not running as root")); }

```

See https://github.com/tarka/rsu/blob/main/tests/lib.rs for an example of use.