Running `cargo test -- --help` doesn't produce expected output

[rockboynton]

Problem

The output of cargo test -- --help first outputs the test output, followed by 2x usage output.
E.g.

user@host:~/projects/adder$ cargo test -- --help
    Finished test [unoptimized + debuginfo] target(s) in 0.00s
     Running unittests (target/debug/deps/adder-bc980f34fe13c9a4)
Usage: --help [OPTIONS] [FILTERS...]

Options:
        --include-ignored 
                        Run ignored and not ignored tests
        --ignored       Run only ignored tests
        --force-run-in-process 
                        Forces tests to run in-process when panic=abort
        --exclude-should-panic 
                        Excludes tests marked as should_panic
        --test          Run tests and not benchmarks
        --bench         Run benchmarks instead of tests
        --list          List all tests and benchmarks
    -h, --help          Display this message
        --logfile PATH  Write logs to the specified file
        --nocapture     don't capture stdout/stderr of each task, allow
                        printing directly
        --test-threads n_threads
                        Number of threads used for running tests in parallel
        --skip FILTER   Skip tests whose names contain FILTER (this flag can
                        be used multiple times)
    -q, --quiet         Display one character per test instead of one line.
                        Alias to --format=terse
        --exact         Exactly match filters rather than by substring
        --color auto|always|never
                        Configure coloring of output:
                        auto = colorize if stdout is a tty and tests are run
                        on serially (default);
                        always = always colorize output;
                        never = never colorize output;
        --format pretty|terse|json|junit
                        Configure formatting of output:
                        pretty = Print verbose output;
                        terse = Display one character per test;
                        json = Output a json document;
                        junit = Output a JUnit document
        --show-output   Show captured stdout of successful tests
    -Z unstable-options Enable nightly-only flags:
                        unstable-options = Allow use of experimental features
        --report-time [plain|colored]
                        Show execution time of each test. Available values:
                        plain = do not colorize the execution time (default);
                        colored = colorize output according to the `color`
                        parameter value;
                        Threshold values for colorized output can be
                        configured via
                        `RUST_TEST_TIME_UNIT`, `RUST_TEST_TIME_INTEGRATION`
                        and
                        `RUST_TEST_TIME_DOCTEST` environment variables.
                        Expected format of environment variable is
                        `VARIABLE=WARN_TIME,CRITICAL_TIME`.
                        Durations must be specified in milliseconds, e.g.
                        `500,2000` means that the warn time
                        is 0.5 seconds, and the critical time is 2 seconds.
                        Not available for --format=terse
        --ensure-time   Treat excess of the test execution time limit as
                        error.
                        Threshold values for this option can be configured via
                        `RUST_TEST_TIME_UNIT`, `RUST_TEST_TIME_INTEGRATION`
                        and
                        `RUST_TEST_TIME_DOCTEST` environment variables.
                        Expected format of environment variable is
                        `VARIABLE=WARN_TIME,CRITICAL_TIME`.
                        `CRITICAL_TIME` here means the limit that should not
                        be exceeded by test.
        --shuffle       Run tests in random order
        --shuffle-seed SEED
                        Run tests in random order; seed the random number
                        generator with SEED


The FILTER string is tested against the name of all tests, and only those
tests whose names contain the filter are run. Multiple filter strings may
be passed, which will run all tests matching any of the filters.

By default, all tests are run in parallel. This can be altered with the
--test-threads flag or the RUST_TEST_THREADS environment variable when running
tests (set it to 1).

By default, the tests are run in alphabetical order. Use --shuffle or set
RUST_TEST_SHUFFLE to run the tests in random order. Pass the generated
"shuffle seed" to --shuffle-seed (or set RUST_TEST_SHUFFLE_SEED) to run the
tests in the same order again. Note that --shuffle and --shuffle-seed do not
affect whether the tests are run in parallel.

All tests have their standard output and standard error captured by default.
This can be overridden with the --nocapture flag or setting RUST_TEST_NOCAPTURE
environment variable to a value other than "0". Logging is not captured by default.

Test Attributes:

    `#[test]`        - Indicates a function is a test to be run. This function
                       takes no arguments.
    `#[bench]`       - Indicates a function is a benchmark to be run. This
                       function takes one argument (test::Bencher).
    `#[should_panic]` - This function (also labeled with `#[test]`) will only pass if
                        the code causes a panic (an assertion failure or panic!)
                        A message may be provided, which the failure string must
                        contain: #[should_panic(expected = "foo")].
    `#[ignore]`       - When applied to a function which is already attributed as a
                        test, then the test runner will ignore these tests during
                        normal test runs. Running with --ignored or --include-ignored will run
                        these tests.
   Doc-tests adder
Usage: --help [OPTIONS] [FILTERS...]

Options:
        --include-ignored 
                        Run ignored and not ignored tests
        --ignored       Run only ignored tests
        --force-run-in-process 
                        Forces tests to run in-process when panic=abort
        --exclude-should-panic 
                        Excludes tests marked as should_panic
        --test          Run tests and not benchmarks
        --bench         Run benchmarks instead of tests
        --list          List all tests and benchmarks
    -h, --help          Display this message
        --logfile PATH  Write logs to the specified file
        --nocapture     don't capture stdout/stderr of each task, allow
                        printing directly
        --test-threads n_threads
                        Number of threads used for running tests in parallel
        --skip FILTER   Skip tests whose names contain FILTER (this flag can
                        be used multiple times)
    -q, --quiet         Display one character per test instead of one line.
                        Alias to --format=terse
        --exact         Exactly match filters rather than by substring
        --color auto|always|never
                        Configure coloring of output:
                        auto = colorize if stdout is a tty and tests are run
                        on serially (default);
                        always = always colorize output;
                        never = never colorize output;
        --format pretty|terse|json|junit
                        Configure formatting of output:
                        pretty = Print verbose output;
                        terse = Display one character per test;
                        json = Output a json document;
                        junit = Output a JUnit document
        --show-output   Show captured stdout of successful tests
    -Z unstable-options Enable nightly-only flags:
                        unstable-options = Allow use of experimental features
        --report-time [plain|colored]
                        Show execution time of each test. Available values:
                        plain = do not colorize the execution time (default);
                        colored = colorize output according to the `color`
                        parameter value;
                        Threshold values for colorized output can be
                        configured via
                        `RUST_TEST_TIME_UNIT`, `RUST_TEST_TIME_INTEGRATION`
                        and
                        `RUST_TEST_TIME_DOCTEST` environment variables.
                        Expected format of environment variable is
                        `VARIABLE=WARN_TIME,CRITICAL_TIME`.
                        Durations must be specified in milliseconds, e.g.
                        `500,2000` means that the warn time
                        is 0.5 seconds, and the critical time is 2 seconds.
                        Not available for --format=terse
        --ensure-time   Treat excess of the test execution time limit as
                        error.
                        Threshold values for this option can be configured via
                        `RUST_TEST_TIME_UNIT`, `RUST_TEST_TIME_INTEGRATION`
                        and
                        `RUST_TEST_TIME_DOCTEST` environment variables.
                        Expected format of environment variable is
                        `VARIABLE=WARN_TIME,CRITICAL_TIME`.
                        `CRITICAL_TIME` here means the limit that should not
                        be exceeded by test.
        --shuffle       Run tests in random order
        --shuffle-seed SEED
                        Run tests in random order; seed the random number
                        generator with SEED


The FILTER string is tested against the name of all tests, and only those
tests whose names contain the filter are run. Multiple filter strings may
be passed, which will run all tests matching any of the filters.

By default, all tests are run in parallel. This can be altered with the
--test-threads flag or the RUST_TEST_THREADS environment variable when running
tests (set it to 1).

By default, the tests are run in alphabetical order. Use --shuffle or set
RUST_TEST_SHUFFLE to run the tests in random order. Pass the generated
"shuffle seed" to --shuffle-seed (or set RUST_TEST_SHUFFLE_SEED) to run the
tests in the same order again. Note that --shuffle and --shuffle-seed do not
affect whether the tests are run in parallel.

All tests have their standard output and standard error captured by default.
This can be overridden with the --nocapture flag or setting RUST_TEST_NOCAPTURE
environment variable to a value other than "0". Logging is not captured by default.

Test Attributes:

    `#[test]`        - Indicates a function is a test to be run. This function
                       takes no arguments.
    `#[bench]`       - Indicates a function is a benchmark to be run. This
                       function takes one argument (test::Bencher).
    `#[should_panic]` - This function (also labeled with `#[test]`) will only pass if
                        the code causes a panic (an assertion failure or panic!)
                        A message may be provided, which the failure string must
                        contain: #[should_panic(expected = "foo")].
    `#[ignore]`       - When applied to a function which is already attributed as a
                        test, then the test runner will ignore these tests during
                        normal test runs. Running with --ignored or --include-ignored will run
                        these tests.

Steps

1. create dummy test project
2. run cargo test -- --help

Possible Solution(s)

No response

Notes

Running Ubuntu (WSL) on Windows

Version

cargo 1.58.0 (f01b232bc 2022-01-19)
release: 1.58.0
commit-hash: f01b232bc7f4d94f0c4603930a5a96277715eb8c
commit-date: 2022-01-19
host: x86_64-unknown-linux-gnu
libgit2: 1.3.0 (sys:0.13.23 vendored)
libcurl: 7.80.0-DEV (sys:0.4.51+curl-7.80.0 vendored ssl:OpenSSL/1.1.1l)
os: Ubuntu 20.04 (focal) [64-bit]

[weihanglo]

The result is, unfortunately, expected. cargo test compiles each test target and links it to libtest, and then run all of them. The usage message you saw are command line options from libtest. Cargo doesn't control those options directly.

You surely could look for -h|--help args and run only one target to show the usage message exactly once. The relevant code is here. Though I still feel like it's unwise to alter CLI options not controlled by cargo itself.

Refs:

• https://doc.rust-lang.org/1.58.1/cargo/reference/cargo-targets.html#tests
• https://doc.rust-lang.org/1.58.1/rustc/tests/
• https://github.com/rust-lang/rust/blob/1.58.1/library/test/src/cli.rs#L47-L193