Crate tracing_capture

Capturing tracing spans and events, e.g. for testing purposes.

The core type in this crate is CaptureLayer, a tracing Layer that can be used to capture tracing spans and events.

Examples

use tracing::Level;
use tracing_subscriber::layer::SubscriberExt;
use tracing_capture::{CaptureLayer, SharedStorage};

let subscriber = tracing_subscriber::fmt()
    .pretty()
    .with_max_level(Level::INFO)
    .finish();
// Add the capturing layer.
let storage = SharedStorage::default();
let subscriber = subscriber.with(CaptureLayer::new(&storage));

// Capture tracing information.
tracing::subscriber::with_default(subscriber, || {
    tracing::info_span!("test", num = 42_i64).in_scope(|| {
        tracing::warn!("I feel disturbance in the Force...");
    });
});

// Inspect the only captured span.
let storage = storage.lock();
assert_eq!(storage.all_spans().len(), 1);
let span = storage.all_spans().next().unwrap();
assert_eq!(span["num"], 42_i64);
assert_eq!(span.stats().entered, 1);
assert!(span.stats().is_closed);

// Inspect the only event in the span.
let event = span.events().next().unwrap();
assert_eq!(*event.metadata().level(), Level::WARN);
assert_eq!(
    event.message(),
    Some("I feel disturbance in the Force...")
);

Alternatives / similar tools

• tracing-test is a lower-level alternative.
• tracing-fluent-assertions is more similar in its goals, but differs significantly in the API design; e.g., the assertions need to be declared before the capture.

Modules

predicates

Predicates for CapturedSpans and CapturedEvents.

Structs

CaptureLayer

Tracing Layer that captures (optionally filtered) spans and events.

CapturedEvent

Captured tracing event containing a reference to its Metadata and values that the event was created with.

CapturedEvents

Iterator over CapturedEvents returned from Storage::all_events() etc.

CapturedSpan

Captured tracing span containing a reference to its Metadata, values that the span was created with, stats, and descendant CapturedEvents.

CapturedSpans

Iterator over CapturedSpans returned from Storage::all_spans() etc.

DescendantEvents

Iterator over the descendant events of a CapturedSpan. Returned by CapturedSpan::descendant_events().

DescendantSpans

Iterator over descendant CapturedSpans of a span. Returned by CapturedSpan::descendants().

SharedStorage

Shared wrapper for tracing Storage.

SpanStats

Statistics about a CapturedSpan.

Storage

Storage of captured tracing information.

Traits

Captured

Uniting trait for CapturedSpans and CapturedEvents that allows writing generic code in cases both should be supported.