Struct TestWriter

pub struct TestWriter { /* private fields */ }

Available 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 = TestWriter

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>

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

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

Flushes 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

where Self: Sized,

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

Layout

Note: Most layout information is completely unstable and may even differ between compilations. The only exception is types with certain repr(...) attributes. Please see the Rust Reference's “Type Layout” chapter for details on type layout guarantees.

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