It seems one cannot use #[tokio-test]
for test async functions in the Rust doc test?
For now I have to write an async main function and tag it with #[tokio-main]
and call test_fn().await
in it to let some async function run during cargo test --doc
.
Is there some other better ways to allow doc tests run as if it is a normal test function, for example with #[tokio-test]
? Also it would be nice if the tag #[tokio-test]
can be shown in the doc, so users can copy the doc and use it as a test directly in their project. (And this probably can be done like ##[tokio-test]
?)
Doc tests automatically wrap the code block in a synchronous fn main() { … }
. .awaiting
requires an asynchronous runtime. You cannot .await
without spawning some sort of a runtime. You could spawn a regular, multi-threaded runtime for each doc test:
/// ```rust
/// #[tokio::main]
/// async fn main() {
/// let len = async { "aaaa".len() }.await;
/// assert_eq!(len, 4);
/// }
/// ```
Spawning a runtime for each doc test is probably not the best idea. A better way would be to use tokio_test::block_on
which uses a test local runtime (similar to #[tokio-test])
to block on the provided future:
/// ```rust
/// let len = tokio_test::block_on( async { "aaaa".len() } );
/// assert_eq!(len, 4);
/// ```
To reduce the boilerplate, you can a macro for block_on
:
macro_rules! bo {
($e:expr) => {
tokio_test::block_on($e)
};
}
And use it like so:
/// ```rust
/// let len = async { "aaaa".len() };
/// assert_eq!(bo!(len), 4)
/// ```
If you want to use asynchronous code in doctests without spawning a new runtime for each you can just wrap the whole doctest instead of just the async part in a tokio_test::block_on
.
Example:
/// Asynchronously get length of "aaaa"
/// ```
/// # tokio_test::block_on(async {
/// let len = async { "aaaa".len() };
/// assert_eq!(len.await, 4)
/// # })
/// ```
I do not know enough about your special use case but maybe you want to avoid the async runtime and wrap your documentation code block like this:
/// ...
/// Example
/// ```rust,no_run // <- try using this `no_run` tag
/// ...
/// #[tokio::main]
/// async fn main() {
/// ...
/// }
/// ...
/// ```
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