CARGO-TEST(1)

📦 version 1.83.0, in ubuntu jammy, ubuntu noble

✨ CARGO-TEST ✨

okay bestie, welcome to cargo-test, straight outta the General Commands Manual (section 1, the classics). this is the page where cargo teaches you how to ✨execute unit and integration tests of a package✨. buckle up, it's a long one, but we're doing it together 🫶

🌸 NAME 🌸

cargo-test — Execute unit and integration tests of a package 💖

🎀 SYNOPSIS 🎀

cargo test [options] [testname] [-- test-options]

🦋 DESCRIPTION 🦋

Compile and execute unit, integration, and documentation tests. that's the whole vibe. compile, run, slay. 💅

The test filtering argument TESTNAME and all the arguments following the two dashes (--) are passed to the test binaries and thus to libtest (rustc's built in unit-test and micro-benchmarking framework). If you're passing arguments to both Cargo and the binary, the ones after -- go to the binary, the ones before go to Cargo. so basically: before the dashes = Cargo's business, after the dashes = the binary's business. no crossover, no drama 🙈

For details about libtest's arguments see the output of cargo test -- --help and check out the rustc book's chapter on how tests work at https://doc.rust-lang.org/rustc/tests/index.html.

As an example, this will filter for tests with foo in their name and run them on 3 threads in parallel:

cargo test foo -- --test-threads 3

Tests are built with the --test option to rustc which creates a special executable by linking your code with libtest. The executable automatically runs all functions annotated with the #[test] attribute in multiple threads. #[bench] annotated functions will also be run with one iteration to verify that they are functional. yes, one single iteration, just a lil vibe check to make sure nothing's broken 👑

If the package contains multiple test targets, each target compiles to a special executable as aforementioned, and then is run serially. one at a time, no cutting in line 🧚

The libtest harness may be disabled by setting harness = false in the target manifest settings, in which case your code will need to provide its own main function to handle running tests. you're on your own for the main function then, bestie, no cap.

📖 Documentation tests 📖

Documentation tests are also run by default, which is handled by rustdoc. It extracts code samples from documentation comments of the library target, and then executes them. so your docs better not be lying, they're getting tested 😭

Different from normal test targets, each code block compiles to a doctest executable on the fly with rustc. These executables run in parallel in separate processes. The compilation of a code block is in fact a part of test function controlled by libtest, so some options such as --jobs might not take effect. Note that this execution model of doctests is not guaranteed and may change in the future; beware of depending on it. ⚠️ fr fr, don't build your whole setup on top of a maybe.

See the rustdoc book https://doc.rust-lang.org/rustdoc/ for more information on writing doc tests.

📂 Working directory of tests 📂

The working directory when running each unit and integration test is set to the root directory of the package the test belongs to. Setting the working directory of tests to the package's root directory makes it possible for tests to reliably access the package's files using relative paths, regardless from where cargo test was executed from. so your relative paths are safe no matter where you ran the command from. iconic, honestly 💖

For documentation tests, the working directory when invoking rustdoc is set to the workspace root directory, and is also the directory rustdoc uses as the compilation directory of each documentation test. The working directory when running each documentation test is set to the root directory of the package the test belongs to, and is controlled via rustdoc's --test-run-directory option.

👑 OPTIONS 👑

💅 Test Options 💅

  • --no-run — Compile, but don't run tests. all the building, none of the running. like getting ready but never leaving the house 💀
  • --no-fail-fast — Run all tests regardless of failure. Without this flag, Cargo will exit after the first executable fails. The Rust test harness will run all tests within the executable to completion, this flag only applies to the executable as a whole. so it's executables-as-a-whole that keep going, not a magic "ignore everything" button.

🍓 Package Selection 🍓

By default, when no package selection options are given, the packages selected depend on the selected manifest file (based on the current working directory if --manifest-path is not given). If the manifest is the root of a workspace then the workspaces default members are selected, otherwise only the package defined by the manifest will be selected.

The default members of a workspace can be set explicitly with the workspace.default-members key in the root manifest. If this is not set, a virtual workspace will include all workspace members (equivalent to passing --workspace), and a non-virtual workspace will include only the root crate itself.

  • -p spec…, --package spec… — Test only the specified packages. See cargo-pkgid(1) for the SPEC format. This flag may be specified multiple times and supports common Unix glob patterns like *, ? and []. However, to avoid your shell accidentally expanding glob patterns before Cargo handles them, you must use single quotes or double quotes around each pattern. quote your globs, bestie, or your shell will eat them before Cargo even gets a bite 🙈
  • --workspace — Test all members in the workspace. the whole crew, together 💖
  • --all — Deprecated alias for --workspace. ⚠️ deprecated! it's giving legacy energy, use --workspace instead.
  • --exclude *SPEC*… — Exclude the specified packages. Must be used in conjunction with the --workspace flag. This flag may be specified multiple times and supports common Unix glob patterns like *, ? and []. However, to avoid your shell accidentally expanding glob patterns before Cargo handles them, you must use single quotes or double quotes around each pattern.

🌈 Target Selection 🌈

When no target selection options are given, cargo test will build the following targets of the selected packages:

  • lib — used to link with binaries, examples, integration tests, and doc tests
  • bins (only if integration tests are built and required features are available)
  • examples — to ensure they compile
  • lib as a unit test
  • bins as unit tests
  • integration tests
  • doc tests for the lib target

The default behavior can be changed by setting the test flag for the target in the manifest settings. Setting examples to test = true will build and run the example as a test, replacing the example's main function with the libtest harness. If you don't want the main function replaced, also include harness = false, in which case the example will be built and executed as-is.

Setting targets to test = false will stop them from being tested by default. Target selection options that take a target by name (such as --example foo) ignore the test flag and will always test the given target.

Doc tests for libraries may be disabled by setting doctest = false for the library in the manifest.

See Configuring a target https://doc.rust-lang.org/cargo/reference/cargo-targets.html#configuring-a-target for more information on per-target settings.

Binary targets are automatically built if there is an integration test or benchmark being selected to test. This allows an integration test to execute the binary to exercise and test its behavior. The CARGO_BIN_EXE_<name> environment variable https://doc.rust-lang.org/cargo/reference/environment-variables.html#environment-variables-cargo-sets-for-crates is set when the integration test is built so that it can use the env macro https://doc.rust-lang.org/std/macro.env.html to locate the executable.

Passing target selection flags will test only the specified targets.

Note that --bin, --example, --test and --bench flags also support common Unix glob patterns like *, ? and []. However, to avoid your shell accidentally expanding glob patterns before Cargo handles them, you must use single quotes or double quotes around each glob pattern. same rule as before: quotes around your globs, always ✨

  • --lib — Test the package's library.
  • --bin *name*… — Test the specified binary. This flag may be specified multiple times and supports common Unix glob patterns.
  • --bins — Test all binary targets. every single one of them, go off 👑
  • --example *name*… — Test the specified example. This flag may be specified multiple times and supports common Unix glob patterns.
  • --examples — Test all example targets.
  • --test *name*… — Test the specified integration test. This flag may be specified multiple times and supports common Unix glob patterns.
  • --tests — Test all targets in test mode that have the test = true manifest flag set. By default this includes the library and binaries built as unittests, and integration tests. Be aware that this will also build any required dependencies, so the lib target may be built twice (once as a unittest, and once as a dependency for binaries, integration tests, etc.). Targets may be enabled or disabled by setting the test flag in the manifest settings for the target. yes, lib gets built twice, that's not a bug, that's just how it is 😭
  • --bench *name*… — Test the specified benchmark. This flag may be specified multiple times and supports common Unix glob patterns.
  • --benches — Test all targets in benchmark mode that have the bench = true manifest flag set. By default this includes the library and binaries built as benchmarks, and bench targets. Be aware that this will also build any required dependencies, so the lib target may be built twice (once as a benchmark, and once as a dependency for binaries, benchmarks, etc.). Targets may be enabled or disabled by setting the bench flag in the manifest settings for the target.
  • --all-targets — Test all targets. This is equivalent to specifying --lib --bins --tests --benches --examples. one flag to rule them all 💅
  • --doc — Test only the library's documentation. This cannot be mixed with other target options. 🚫 do NOT combine this one, it said what it said.

💜 Feature Selection 💜

The feature flags allow you to control which features are enabled. When no feature options are given, the default feature is activated for every selected package.

See the features documentation https://doc.rust-lang.org/cargo/reference/features.html#command-line-feature-options for more details.

  • -F features, --features features — Space or comma separated list of features to activate. Features of workspace members may be enabled with package-name/feature-name syntax. This flag may be specified multiple times, which enables all specified features.
  • --all-features — Activate all available features of all selected packages. everything, everywhere, all at once ✨
  • --no-default-features — Do not activate the default feature of the selected packages. the default feature said "not today" 🙈

⭐ Compilation Options ⭐

  • --target triple — Test for the given architecture. The default is the host architecture. The general format of the triple is <arch><sub>-<vendor>-<sys>-<abi>. Run rustc --print target-list for a list of supported targets. This flag may be specified multiple times.

This may also be specified with the build.target config value https://doc.rust-lang.org/cargo/reference/config.html.

Note that specifying this flag makes Cargo run in a different mode where the target artifacts are placed in a separate directory. See the build cache https://doc.rust-lang.org/cargo/reference/build-cache.html documentation for more details.

  • -r, --release — Test optimized artifacts with the release profile. See also the --profile option for choosing a specific profile by name.
  • --profile name — run your tests with the profile called name, bestie. Peep the reference at https://doc.rust-lang.org/cargo/reference/profiles.html for the whole tea on profiles. 💅
  • --timings=fmts — this one spills how long every compilation took and tracks concurrency information over time. You can give it an optional comma-separated list of output formats. If you just say --timings with no argument, it defaults to --timings=html. Lowkey important: specifying an output format (instead of just using the default) is unstable and needs -Zunstable-options. Valid output formats are:
    • html (unstable, requires -Zunstable-options) — writes a human-readable file called cargo-timing.html into the target/cargo-timings directory, with a whole report of the compilation. It also writes a report to that same directory with a timestamp in the filename, so you can look back at older runs. HTML output is for human eyes only, and does not provide machine-readable timing data. 🎀
    • json (unstable, requires -Zunstable-options) — emits machine-readable JSON information about timing information. ✨

🦋 Output Options 🦋

  • --target-dir directory — directory for all generated artifacts and intermediate files. May also be specified with the CARGO_TARGET_DIR environment variable, or the build.target-dir config value at https://doc.rust-lang.org/cargo/reference/config.html. Defaults to target in the root of the workspace. 📁

💖 Display Options 💖

By default the Rust test harness hides output from test execution to keep results readable. Test output can be recovered (e.g., for debugging) by passing --nocapture to the test binaries:

cargo test -- --nocapture
  • -v, --verbose — use verbose output. May be specified twice for “very verbose” output which includes extra output such as dependency warnings and build script output. May also be specified with the term.verbose config value at https://doc.rust-lang.org/cargo/reference/config.html. 👑
  • -q, --quiet — do not print cargo log messages. May also be specified with the term.quiet config value at https://doc.rust-lang.org/cargo/reference/config.html. 🤫
  • --color when — control when colored output is used. Valid values:
    • auto (default): automatically detect if color support is available on the terminal. 🌈
    • always: always display colors. 💖
    • never: never display colors. 🚫

May also be specified with the term.color config value at https://doc.rust-lang.org/cargo/reference/config.html.

  • --message-format fmt — the output format for diagnostic messages. Can be specified multiple times and consists of comma-separated values. Valid values:
    • human (default): display in a human-readable text format. Conflicts with short and json.
    • short: emit shorter, human-readable text messages. Conflicts with human and json.
    • json: emit JSON messages to stdout. See the reference at https://doc.rust-lang.org/cargo/reference/external-tools.html#json-messages for more details. Conflicts with human and short.
    • json-diagnostic-short: ensure the rendered field of JSON messages contains the “short” rendering from rustc. Cannot be used with human or short.
    • json-diagnostic-rendered-ansi: ensure the rendered field of JSON messages contains embedded ANSI color codes for respecting rustc’s default color scheme. Cannot be used with human or short.
    • json-render-diagnostics: instruct Cargo to not include rustc diagnostics in JSON messages printed, but instead Cargo itself should render the JSON diagnostics coming from rustc. Cargo’s own JSON diagnostics and others coming from rustc are still emitted. Cannot be used with human or short.

📜 Manifest Options 📜

  • --manifest-path path — path to the Cargo.toml file. By default, Cargo searches for the Cargo.toml file in the current directory or any parent directory. 🔍
  • --ignore-rust-version — ignore rust-version specification in packages. 🙈
  • --locked — asserts that the exact same dependencies and versions are used as when the existing Cargo.lock file was originally generated. Cargo will exit with an error when either of the following scenarios arises:
    • The lock file is missing.
    • Cargo attempted to change the lock file due to a different dependency resolution.

It may be used in environments where deterministic builds are desired, such as in CI pipelines. 🧪

  • --offline — prevents Cargo from accessing the network for any reason. Without this flag, Cargo will stop with an error if it needs to access the network and the network is not available. With this flag, Cargo will attempt to proceed without the network if possible.

Beware that this may result in different dependency resolution than online mode. Cargo will restrict itself to crates that are downloaded locally, even if there might be a newer version as indicated in the local copy of the index. See the cargo-fetch(1) command to download dependencies before going offline.

May also be specified with the net.offline config value at https://doc.rust-lang.org/cargo/reference/config.html.

  • --frozen — equivalent to specifying both --locked and --offline. ❄️
  • --lockfile-path PATH — changes the path of the lockfile from the default (<workspace_root>/Cargo.lock) to PATH. PATH must end with Cargo.lock (e.g. --lockfile-path /tmp/temporary-lockfile/Cargo.lock). Note that providing --lockfile-path will ignore existing lockfile at the default path, and instead will either use the lockfile from PATH, or write a new lockfile into the provided PATH if it doesn’t exist. This flag can be used to run most commands in read-only directories, writing lockfile into the provided PATH.

This option is only available on the nightly channel at https://doc.rust-lang.org/book/appendix-07-nightly-rust.html and requires the -Z unstable-options flag to enable (see #14421 at https://github.com/rust-lang/cargo/issues/14421).

🫶 Common Options 🫶

  • +toolchain — if Cargo has been installed with rustup, and the first argument to cargo begins with +, it will be interpreted as a rustup toolchain name (such as +stable or +nightly). See the rustup documentation at https://rust-lang.github.io/rustup/overrides.html for more information about how toolchain overrides work. 🛠️
  • --config KEY=VALUE or PATH — overrides a Cargo configuration value. The argument should be in TOML syntax of KEY=VALUE, or provided as a path to an extra configuration file. This flag may be specified multiple times. See the command-line overrides section at https://doc.rust-lang.org/cargo/reference/config.html#command-line-overrides for more information. ⚙️
  • -C PATH — changes the current working directory before executing any specified operations. This affects things like where cargo looks by default for the project manifest (Cargo.toml), as well as the directories searched for discovering .cargo/config.toml, for example. This option must appear before the command name, for example cargo -C path/to/my-project build.

This option is only available on the nightly channel at https://doc.rust-lang.org/book/appendix-07-nightly-rust.html and requires the -Z unstable-options flag to enable (see #10098 at https://github.com/rust-lang/cargo/issues/10098).

  • -h, --help — prints help information. 🆘
  • -Z flag — unstable (nightly-only) flags to Cargo. Run cargo -Z help for details. 🌙

💅 Miscellaneous Options 💅

The --jobs argument affects the building of the test executable but does not affect how many threads are used when running the tests. The Rust test harness includes an option to control the number of threads used:

cargo test -j 2 -- --test-threads=2
  • -j N, --jobs N — number of parallel jobs to run. May also be specified with the build.jobs config value at https://doc.rust-lang.org/cargo/reference/config.html. Defaults to the number of logical CPUs. If negative, it sets the maximum number of parallel jobs to the number of logical CPUs plus provided value. If a string default is provided, it sets the value back to defaults. Should not be 0. 🚫
  • --future-incompat-report — displays a future-incompat report for any future-incompatible warnings produced during execution of this command

See cargo-report(1)

While cargo test involves compilation, it does not provide a --keep-going flag. Use --no-fail-fast to run as many tests as possible without stopping at the first failure. To “compile” as many tests as possible, use --tests to build test binaries separately. For example:

cargo build --tests --keep-going
cargo test --tests --no-fail-fast

🌈 ENVIRONMENT 🌈

See the reference at https://doc.rust-lang.org/cargo/reference/environment-variables.html for details on environment variables that Cargo reads. 🌱

💀 EXIT STATUS 💀

  • 0: Cargo succeeded. 🎉
  • 101: Cargo failed to complete. 😭

✨ EXAMPLES ✨

  1. Execute all the unit and integration tests of the current package:
cargo test
  1. Run only tests whose names match against a filter string:
cargo test name_filter
  1. Run only a specific test within a specific integration test:
cargo test --test int_test_name -- modname::test_name

👑 SEE ALSO 👑

That’s the whole page, bestie. The footer says CARGO-TEST(1) — that’s the source/version/date moment, and it’s iconic. Now go run those tests. 💖

📦 where this page comes from