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I'm writing a Rust program where I do manual command-line argument parsing. I skip the first argument since that's the executable and I don't care about that, then check the second argument for what subcommand to run. Then I pass on the rest of env::Args to that subcommand's function for parsing of the subcommand arguments.

Now, I want to add some tests that test the entire subcommands to see if they do what's expected of them—a bit like integration tests except within the codebase. However, I can't find any way to construct my own env::Args. Is this something that's possible? I had a look at a similar question about replacing an entry in env::Args but it seems that's impossible.

Is there any way I can achieve what I want, i.e. testing of my subcommand functions that take an env::Args by providing a forged one?

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    No. But you can easily give the command a Vec. Commented Nov 10 at 11:09

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I ended up solving this by changing the signature of the subcommands from directly taking an env::Args

fn cmd_something(arguments: env::Args) -> ExitCode { ... }

to taking any type that implements IntoIterator where the item type is String:

fn cmd_something<I: IntoIterator<Item = String>>(arguments: I) -> ExitCode { ... }

This allows me to both call the function with env::Args and arrays or Vecs, so that in tests I can do something like this:

let arguments = ["testdata/testfile.txt".to_string()];

assert_eq!(cmd_something(arguments), ExitCode::SUCCESS);

Which is very convenient. This works because both std::Env and Vec implement the IntoIterator trait.

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