How to Enable Real-time/Streaming Output for Tests with rustaceanvim using RustLsp("run")?

[SamuelBorn]

Hi everyone,

I'm using rustaceanvim and trying to get test output to stream in real-time, similar to how cargo test MYTESTNAME behaves in the terminal.

Currently, when I'm on a test function (e.g., #[test] fn my_test() { ... }) and execute vim.cmd.RustLsp("run"), the output (like println! statements from the test) seems to be collected in the background and is only printed all at once after the test completes.

Interestingly, if I use vim.cmd.RustLsp("run") on my main function, the output streams live as expected.

What I'm trying to achieve:
I want the output from my tests run via vim.cmd.RustLsp("run") to also appear in real-time, line by line, as it's generated.

Steps I'm taking:

1. Start Neovim with a minimal configuration: nvim -u repro.lua (default one).
2. Open a Rust project.
3. Navigate the cursor to be within a test function.
4. Execute the command vim.cmd.RustLsp("run").

Example Code

// Prints in real time!
fn main() {
    println!("Hello, world!");
    std::thread::sleep(std::time::Duration::from_secs(3));
    println!("Goodbye, world!");
}

#[cfg(test)]
mod test {
    
    // Does not print in real time!
    #[test]
    fn name() {

        super::main();
    }
}

Example Code

vim.env.LAZY_STDPATH = '.repro'
load(vim.fn.system('curl -s https://raw.githubusercontent.com/folke/lazy.nvim/main/bootstrap.lua'))()

require('lazy.minit').repro {
  spec = {
    {
      'mrcjkb/rustaceanvim',
      version = '^6',
      init = function()
        -- This did not help!
        -- vim.g.rustaceanvim = { tools = { test_executor = 'background' } }
      end,
      lazy = false,
    },
  },
}

Neovim version (nvim -v)

v0.11.1

Operating system/version

Fedora Linux 42

Output of :checkhealth rustaceanvim

==============================================================================
rustaceanvim:                           require("rustaceanvim.health").check()

Checking for Lua dependencies ~
- ✅ OK optional dependency nvim-dap not installed. Needed for debugging features [mfussenegger/nvim-dap](https://github.com/mfussenegger/nvim-dap)

Checking external dependencies ~
- ✅ OK rust-analyzer: found rust-analyzer 1.86.0
- ✅ OK Cargo: found cargo 1.86.0 (adf9b6ad1 2025-02-28)
- ✅ OK rustc: found rustc 1.86.0 (05f9846f8 2025-03-31) (Fedora 1.86.0-1.fc42)

Checking config ~
- ✅ OK No errors found in config.

Checking for conflicting plugins ~
- ✅ OK No conflicting plugins detected.

Checking for tree-sitter parser ~
- ✅ OK tree-sitter parser for Rust detected.

[mrcjkb]

Hey 👋

By default, cargo test captures stdout, to keep test output tidy. If you run cargo test in a terminal, you'll observe the same behaviour.
With the cargo CLI, you can disable this behaviour by passing --nocapture to the test executable: cargo test -- --nocapture.
With the :RustLsp run command, you can just append the flag:

:RustLsp run --nocapture

Or, in Lua:

vim.cmd.RustLsp { "run", "--nocapture" }

[SamuelBorn]

Argggh. Yeah, my bad! I forgot I always pass --nocapture by default.

Thank you!

[SamuelBorn]

Ahh no this has an unwanted side effect unfortunately.

I have this keyboard shortcut { "<leader>tt", function() vim.cmd.RustLsp("run", "--nocapture") end } now.
But with this always all tests are executed where as { "<leader>tt", function() vim.cmd.RustLsp("run") end } only runs the test under my cursor

[mrcjkb]

That's a bug.

#759

[SamuelBorn]

Thank you! Pulled down the latest commit. No everything works as expected.