How to limit the number of test threads in Cargo.toml?

Question

I have tests which share a common resource and can't be executed concurrently. These tests fail with cargo test , but work with RUST_TEST_THREADS=1 cargo test .

I can modify the tests to wait on a global mutex, but I don't want to clutter them if there is any simpler way to force cargo set this environment variable for me.

Answer 1

As of Rust 1.18, there is no such thing. In fact, there is not even a simpler option to disable parallel testing.
Source

However, what might help you is cargo test -- --test-threads=1 , which is the recommended way of doing what you are doing over the RUST_TEST_THREADS envvar. Keep in mind that this only sets the number of threads used for testing in addition to the main thread.