How to write and publish reusable steps?

[ms-ati]

Hi! I am working on a port of cucumber/aruba to cucumber-rs, to be called aruba-rs.

For anyone not familiar: Aruba, written in Ruby, is a supported part of Cucumber which provides a super useful set of Step Definitions and tools for testing command-line applications. I'd like to have these step definitions available when working on command-line applications in Rust in a way that is well-integrated and designed. Why? I've observed:

• A lot command-line applications being written in Rust
• A lack of common executable specification practices, leading to avoidable failure reports
• Similar patterns for using cucumber-rs to write specs for command-line apps, with unique issues and unforeseen edgecases, across many projects.

Wouldn't it be awesome if aruba-rs would lead to low-friction, widespread reuse of a shared set of step definitions for the executable specifications of command-line apps across the Rust ecosystem? 🙏🏻 🎈

However, to get there, I have some questions! 😄

(1) How can a dev-dependency library publish reusable Step Definitions that require state?

The challenge: As I understand it (please correct if I've misunderstood!), the design of cucumber-rs is for the step definition macros given/when/then to require, as their first parameter, a concrete struct for which we have already derived cucumber::World via a derive macro.

Q: How should a library such as aruba-rs make reusable step definitions available, where each step would need to know the ultimate concrete type of the World parameter, and access a common sub-set of state from it?

Assumption: I'll need to use the World parameter to access all mutable state about processes we have launched in the previous steps of any Scenario, for example:

Feature: Help text

  Scenario: If we pass the `--help` flag, we see usage documentation
    When I run `aruba_hello_world --help`
    Then the exit status should be 0
     And the stdout contains: "Usage: "

trait ArubaWorld {
    fn last_command_run(&self) -> &Option<std::process::Command>
}

(2) How can .feature files in a project reference Step Definitions from a dev-dependency library?

Thanks for any ideas!

[ilslv]

Very interesting use-case, thanks for bringing that up. I've created a separate repository as an example: https://github.com/ilslv/cucumber-steps-as-library

How can a dev-dependency library publish reusable Step Definitions that require state?

You should create a library, that depends on cucumber and exports World implementor with some step definitions. In example repo this is the /steps directory. In case you need additional steps, downstream crates can add them to an existing World implementor from another crate (/tests/cucumber.rs has an example).

The main limitation is that World implementor can't have generics, so I would advice adding something like anymap to it, so users could dynamically extend World.