Struct tracing_subscriber::fmt::TestWriter

pub struct TestWriter { /* fields omitted */ }

This is supported on crate features fmt and std only.

A writer intended to support libtest’s output capturing for use in unit tests.

TestWriter is used by fmt::Subscriber or fmt::Layer to enable capturing support.

cargo test can only capture output from the standard library’s print! macro. See libtest’s output capturing for more details about output capturing.

Writing to io::stdout and io::stderr produces the same results as using libtest’s --nocapture option which may make the results look unreadable.

Implementations

impl TestWriter

pub fn new() -> Self

Returns a new TestWriter with the default configuration.

Trait Implementations

impl Debug for TestWriter

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

Formats the value using the given formatter.

impl Default for TestWriter

fn default() -> TestWriter

Returns the “default value” for a type.

impl<'a> MakeWriter<'a> for TestWriter

type Writer = Self

The concrete io::Write implementation returned by make_writer.

fn make_writer(&'a self) -> Self::Writer

Returns an instance of Writer.

fn make_writer_for(&'a self, meta: &Metadata<'_>) -> Self::Writer

Returns a Writer for writing data from the span or event described by the provided Metadata.

impl Write for TestWriter

fn write(&mut self, buf: &[u8]) -> Result<usize>

Write a buffer into this writer, returning how many bytes were written.

fn flush(&mut self) -> Result<()>

Flush this output stream, ensuring that all intermediately buffered contents reach their destination.

fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> Result<usize, Error>

Like write, except that it writes from a slice of buffers.

fn is_write_vectored(&self) -> bool

🔬 This is a nightly-only experimental API. (can_vector #69941)

Determines if this Writer has an efficient write_vectored implementation.

fn write_all(&mut self, buf: &[u8]) -> Result<(), Error>

Attempts to write an entire buffer into this writer.

fn write_all_vectored(&mut self, bufs: &mut [IoSlice<'_>]) -> Result<(), Error>

🔬 This is a nightly-only experimental API. (write_all_vectored #70436)

Attempts to write multiple buffers into this writer.

fn write_fmt(&mut self, fmt: Arguments<'_>) -> Result<(), Error>

Writes a formatted string into this writer, returning any error encountered.

fn by_ref(&mut self) -> &mut Self

Creates a “by reference” adapter for this instance of Write.