Struct TracingCollector 

pub struct TracingCollector { /* private fields */ }

TracingCollector creates a tracing subscriber that collects a copy of all traces into a buffer. These traces can be retrieved by calling its Display implementation, i.e. calling log.to_string() or format!("{log}"). This is useful for testing with insta snapshots.

IMPORTANT! TracingCollector is meant for use when testing. It collects logs into a memory buffer which keeps growing until it is read, the program exits or it is dropped. This means that if you are using TracingCollector in production the program will eventually run out of memory.

When the TracingCollector is dropped, the buffer is emptied and the tracing subscriber is released but the memory equivalent of a Mutex and an empty Vec is leaked.

When reading the traces, they are stripped of ANSI escape codes and prefixed with a ㏒ character. The former allows the use of colored & formatted terminal output when the test fails or is run with --nocapture and the latter makes the insta inline snapshots work since rust’s r### raw string literals strips leading whitespace. The prefix can be changed or removed using the set_prefix and remove_prefix methods.

Example:

#[test]
fn test_logs() {
    let log = TracingCollector::init_debug_level();
    tracing::info!("First log");

    insta::assert_display_snapshot!(log, @r###"
    ㏒   INFO  First log
        at tests/test.rs:6

    "###);

    tracing::debug!("Second log");
    tracing::info!("Third log");

    insta::assert_display_snapshot!(log, @r###"
    ㏒  DEBUG  Second log
        at tests/test.rs:14

      INFO  Third log
       at tests/test.rs:15

   "###);
}

Implementations

impl TracingCollector

pub fn set_prefix(&mut self, prefix: char)

pub fn remove_prefix(&mut self)

pub fn init_trace_level() -> Self

Create a TracingCollector that collects traces up to the TRACE level.

pub fn init_debug_level() -> Self

Create a TracingCollector that collects traces up to the DEBUG level.

pub fn init_info_level() -> Self

Create a TracingCollector that collects traces up to the INFO level.

pub fn init(max_level: Level) -> Self

Create a new TracingCollector that collects traces up to the specified level.

pub fn clear(&self)

Trait Implementations

impl Display for TracingCollector

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Drop for TracingCollector

fn drop(&mut self)

Executes the destructor for this type.