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mock: add README to tracing-mock (#2362)
## Motivation There has been interest around publishing `tracing-mock` to crates.io for some time. In order to make this possible, documentation and some code clean up is needed. Specifically **I** want to have access to `tracing-mock` within parts of `tokio` to write tests that ensure that the correct calling location is picked up for all `spawn*` functions when the `tracing` feature is enabled. ## Solution This change starts that process by adding a README for `tracing-mock`. The README follows the standard format for all `tracing` crates and includes 2 examples. The README is included in the `lib.rs` docs using `#[doc = include_str!(...)]`, so that the same documentation is included in the crate, and the examples are tested when running doctests. The README describes steps when using the `tracing` 1.0 from crates.io and `tracing-mock` from the `v0.1.x` branch. The tests target the current branch. Co-authored-by: David Barsky <me@davidbarsky.com> Co-authored-by: Eliza Weisman <eliza@buoyant.io>
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![Tracing — Structured, application-level diagnostics][splash] | ||
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[splash]: https://github.com/tokio-rs/tracing/master/assets/splash.svg | ||
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# tracing-mock | ||
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Utilities for testing [`tracing`][tracing] and crates that uses it. | ||
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[![Documentation (master)][docs-master-badge]][docs-master-url] | ||
[![MIT licensed][mit-badge]][mit-url] | ||
[![Build Status][actions-badge]][actions-url] | ||
[![Discord chat][discord-badge]][discord-url] | ||
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[Documentation][docs-master-url] | [Chat][discord-url] | ||
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[docs-master-badge]: https://img.shields.io/badge/docs-master-blue | ||
[docs-master-url]: https://tracing-rs.netlify.com/tracing_mock | ||
[mit-badge]: https://img.shields.io/badge/license-MIT-blue.svg | ||
[mit-url]: https://github.com/tokio-rs/tracing/blob/master/tracing-mock/LICENSE | ||
[actions-badge]: https://github.com/tokio-rs/tracing/workflows/CI/badge.svg | ||
[actions-url]:https://github.com/tokio-rs/tracing/actions?query=workflow%3ACI | ||
[discord-badge]: https://img.shields.io/discord/500028886025895936?logo=discord&label=discord&logoColor=white | ||
[discord-url]: https://discord.gg/EeF3cQw | ||
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## Overview | ||
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[`tracing`] is a framework for instrumenting Rust programs to collect | ||
structured, event-based diagnostic information. `tracing-mock` provides | ||
tools for making assertions about what `tracing` diagnostics are emitted | ||
by code under test. | ||
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*Compiler support: [requires `rustc` 1.49+][msrv]* | ||
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[msrv]: #supported-rust-versions | ||
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## Usage | ||
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`tracing-mock` crate provides a mock | ||
[`Collector`](https://tracing-rs.netlify.app/tracing/#collectors) | ||
that allows asserting on the order and contents of | ||
[spans](https://tracing-rs.netlify.app/tracing/#spans) and | ||
[events](https://tracing-rs.netlify.app/tracing/#events). | ||
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As `tracing-mock` isn't available on [crates.io](https://crates.io/) | ||
yet, you must import it via git. When using `tracing-mock` with the | ||
`tracing` `0.1` ecosystem, it is important that you also override the | ||
source of any `tracing` crates that are transient dependencies. For | ||
example, the `Cargo.toml` for your test crate could contain: | ||
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```toml | ||
[dependencies] | ||
lib-under-test = "1.0" # depends on `tracing` | ||
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[dev-dependencies] | ||
tracing-mock = { git = "https://github.com/tokio-rs/tracing", branch = "v0.1.x", version = "0.1" } | ||
tracing = { git = "https://github.com/tokio-rs/tracing", branch = "v0.1.x", version = "0.1" } | ||
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[patch.crates-io] | ||
tracing = { git = "https://github.com/tokio-rs/tracing", branch = "v0.1.x" } | ||
tracing-core = { git = "https://github.com/tokio-rs/tracing", branch = "v0.1.x" } | ||
``` | ||
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## Examples | ||
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The following examples are for the `master` branch. For examples that | ||
will work with `tracing` from [crates.io], please check the | ||
[v0.1.x](https://github.com/tokio-rs/tracing/tree/v0.1.x/tracing-mock) | ||
branch. | ||
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Below is an example that checks that an event contains a message: | ||
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```rust | ||
use tracing::collect::with_default; | ||
use tracing_mock::{collector, expect, field}; | ||
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fn yak_shaving() { | ||
tracing::info!("preparing to shave yaks"); | ||
} | ||
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let (collector, handle) = collector::mock() | ||
.event(expect::event().with_fields(field::msg("preparing to shave yaks"))) | ||
.only() | ||
.run_with_handle(); | ||
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with_default(collector, || { | ||
yak_shaving(); | ||
}); | ||
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handle.assert_finished(); | ||
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``` | ||
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Below is a slightly more complex example. `tracing-mock` asserts that, in order: | ||
- a span is created with a single field/value pair | ||
- the span is entered | ||
- an event is created with the field `number_of_yaks`, a corresponding | ||
value of 3, and the message "preparing to shave yaks", and nothing else | ||
- an event is created with the field `all_yaks_shaved`, a corresponding value | ||
of `true`, and the message "yak shaving completed" | ||
- the span is exited | ||
- no further traces are received | ||
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```rust | ||
use tracing::collect::with_default; | ||
use tracing_mock::{collector, expect, field}; | ||
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#[tracing::instrument] | ||
fn yak_shaving(number_of_yaks: u32) { | ||
tracing::info!(number_of_yaks, "preparing to shave yaks"); | ||
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let number_shaved = number_of_yaks; // shave_all | ||
tracing::info!( | ||
all_yaks_shaved = number_shaved == number_of_yaks, | ||
"yak shaving completed." | ||
); | ||
} | ||
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let yak_count: u32 = 3; | ||
let span = expect::span().named("yak_shaving"); | ||
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let (collector, handle) = collector::mock() | ||
.new_span( | ||
span.clone() | ||
.with_field(expect::field("number_of_yaks").with_value(&yak_count).only()), | ||
) | ||
.enter(span.clone()) | ||
.event( | ||
expect::event().with_fields( | ||
expect::field("number_of_yaks") | ||
.with_value(&yak_count) | ||
.and(field::msg("preparing to shave yaks")) | ||
.only(), | ||
), | ||
) | ||
.event( | ||
expect::event().with_fields( | ||
expect::field("all_yaks_shaved") | ||
.with_value(&true) | ||
.and(field::msg("yak shaving completed.")) | ||
.only(), | ||
), | ||
) | ||
.exit(span.clone()) | ||
.only() | ||
.run_with_handle(); | ||
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with_default(collector, || { | ||
yak_shaving(yak_count); | ||
}); | ||
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handle.assert_finished(); | ||
``` | ||
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## Supported Rust Versions | ||
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Tracing is built against the latest stable release. The minimum supported | ||
version is 1.49. The current Tracing version is not guaranteed to build on Rust | ||
versions earlier than the minimum supported version. | ||
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Tracing follows the same compiler support policies as the rest of the Tokio | ||
project. The current stable Rust compiler and the three most recent minor | ||
versions before it will always be supported. For example, if the current stable | ||
compiler version is 1.45, the minimum supported version will not be increased | ||
past 1.42, three minor versions prior. Increasing the minimum supported compiler | ||
version is not considered a semver breaking change as long as doing so complies | ||
with this policy. | ||
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## License | ||
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This project is licensed under the [MIT license][mit-url]. | ||
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### Contribution | ||
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Unless you explicitly state otherwise, any contribution intentionally submitted | ||
for inclusion in Tracing by you, shall be licensed as MIT, without any additional | ||
terms or conditions. |
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#![doc = include_str!("../README.md")] | ||
use std::{ | ||
pin::Pin, | ||
task::{Context, Poll}, | ||
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