CARGO-TEST(1)

📦 version 1.89.0, in ubuntu jammy, ubuntu noble

CARGO-TEST(1) 💖

the manual page for cargo test — yes bestie, the one that runs ALL ur tests 🧚✨

(this is the General Commands Manual section of the cargo fam, and honestly? iconic.)</purl>

✨ NAME ✨

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

🦋 SYNOPSIS 🦋

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

💜 DESCRIPTION 💜

okay so. cargo test compiles AND executes ur unit tests, ur integration tests, and ur documentation tests. all of them. it's giving "full coverage era". 💅

The test filtering argument TESTNAME and every single argument after the two dashes (--) get passed straight to the test binaries, which means they go to libtest — that's rustc's built-in unit-test and micro-benchmarking framework, no cap. So if you're throwing arguments at both Cargo and the binary: the ones after -- go to the binary, the ones before go to Cargo. Periodt.

for the deets on libtest's own arguments, go look at the output of cargo test -- --help and also check out the rustc book's chapter on how tests work at <https://doc.rust-lang.org/rustc/tests/index.html> 📖

Example time, bestie — this filters for tests with foo in their name and runs 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 ur code with libtest. That executable automatically runs every function annotated with the #[test] attribute across multiple threads. and the #[bench]-annotated functions? they also get run, with one iteration, just to verify they're functional. slay. 🔥

If the package contains multiple test targets, each target compiles into its own special executable like we said, and then they run serially.

The libtest harness can be turned off by setting harness = false in the target manifest settings — in which case ur code has to provide its own main function to handle running the tests. ur problem now, bestie. 🙈

🌸 Documentation tests 🌸

Documentation tests run by default too, and they're handled by rustdoc. What rustdoc does: it extracts code samples from the documentation comments of the library target, and then executes them. it's giving "ur docs are also ur tests". ✨

Different from normal test targets tho — 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 actually a part of the test function controlled by libtest, so some options — like --jobs — might not take effect. 👀

⚠️ heads up: this execution model of doctests is not guaranteed and may change in the future. so beware of depending on it. fr fr.

See the rustdoc book <https://doc.rust-lang.org/rustdoc/> for more info on writing doc tests. 💖

🎀 Working directory of tests 🎀

When each unit and integration test runs, its working directory is set to the root directory of the package the test belongs to. Setting it to the package's root directory makes it possible for tests to reliably access the package's files using relative paths — regardless of where you ran cargo test from. cute AND functional. 🌈

For documentation tests: the working directory when invoking rustdoc is set to the workspace root directory, and that's 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 it's controlled via rustdoc's --test-run-directory option.

💅 OPTIONS 💅

🔥 Test Options 🔥

  • --no-run — Compile, but don't run the tests. build only, no running, we're just vibing.
  • --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.

🫶 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 isn't given). If the manifest is the root of a workspace, then the workspace's default members are selected — otherwise only the package defined by the manifest gets selected.

The default members of a workspace can be set explicitly with the workspace.default-members key in the root manifest. If that's 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. iykyk.

  • -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 ur shell accidentally expanding glob patterns before Cargo handles them, you must use single quotes or double quotes around each pattern. 💀 (the shell is not ur friend here)
  • --workspace — Test all members in the workspace.
  • --all — Deprecated alias for --workspace.
  • --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 ur 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 stops them from being tested by default. Target selection options that take a target by name (like --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 info on per-target settings. 📚

Binary targets are automatically built if there's an integration test or benchmark being selected to test — this lets an integration test 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 bestie: --bin, --example, --test and --bench flags also support common Unix glob patterns like *, ? and []. However — to avoid ur shell accidentally expanding glob patterns before Cargo handles them, you must use single quotes or double quotes around each glob pattern.
  • --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.
  • --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 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.
  • --bench *name*… — Test the specified benchmark. This flag may be specified multiple times and supports common Unix glob patterns.
  • --benches — Test all targets 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.
  • --doc — Test only the library's documentation. This cannot be mixed with other target options. pick a lane bestie.

💜 Feature Selection 💜

The feature flags let you 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. stacking features like stacking jewelry. 💎
  • --all-features — Activate all available features of all selected packages. all of them. every single one. 👑
  • --no-default-features — Do not activate the default feature of the selected packages.

⭐ 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. 🔥

to be continued, bestie… 💖

  • --profile name — test with the profile you name. Wanna know what profiles even are? The reference got you: https://doc.rust-lang.org/cargo/reference/profiles.html 💜
  • --timings=fmts — spills the tea on how long every single compilation took, plus it tracks concurrency over time. You can pass a comma-separated list of output formats, and ngl --timings with no argument just defaults to --timings=html. Heads up bestie: actually specifying a format (instead of riding the default) is unstable and needs -Zunstable-options. Valid formats:
    • html (unstable, requires -Zunstable-options) — writes a human-readable file cargo-timing.html into the target/cargo-timings directory with a report of the compilation. It also drops a report in that same directory with a timestamp baked into the filename, so you can go back and snoop on older runs. This one is for human eyes only — it does not give you machine-readable timing data. 🙈
    • json (unstable, requires -Zunstable-options) — emits machine-readable JSON info about timing. That's the one for your tools. ✨

🎀 Output Options 🎀

  • --target-dir directory — the directory where all the generated artifacts and intermediate files go. You can also set this with the CARGO_TARGET_DIR environment variable, or with 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 👑

Okay so by default the Rust test harness hides output from test execution, because otherwise results would be a whole mess to read. But you can totally get that output back (say, for debugging) by passing --nocapture to the test binaries:

cargo test -- --nocapture
  • -v, --verbose — verbose output, periodt. Pass it twice for "very verbose" output, which includes extra stuff like 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 — controls when colored output gets used. Valid values:
    • auto (default): automatically detects if your terminal supports color.
    • always: always shows colors, no matter what. 🌈
    • never: never shows 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 it's made of comma-separated values. Valid values:
    • human (default): displays in a human-readable text format. Conflicts with short and json.
    • short: emits shorter, human-readable text messages. Conflicts with human and json.
    • json: emits 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: makes sure the rendered field of JSON messages contains the "short" rendering from rustc. Cannot be used with human or short.
    • json-diagnostic-rendered-ansi: makes sure the rendered field of JSON messages contains embedded ANSI color codes, so it respects rustc's default color scheme. Cannot be used with human or short.
    • json-render-diagnostics: tells Cargo not to include rustc diagnostics in the JSON messages it prints, and instead have Cargo itself 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 the rust-version specification in packages. Yeah, we're ignoring it. Iconic, honestly.
  • --locked — asserts that the exact same dependencies and versions get used as when the existing Cargo.lock file was originally generated. Cargo will exit with an error when either of these scenarios pops up:
    • The lock file is missing. 😭
    • Cargo attempted to change the lock file due to a different dependency resolution.

You'd use this in environments where you want deterministic builds, like in CI pipelines. No surprises allowed. 🔒

  • --offline — stops Cargo from accessing the network for any reason. Without this flag, Cargo will stop with an error if it needs the network and the network isn't available. With this flag, Cargo will try to proceed without the network if it possibly can.

Careful though bestie — this can result in a different dependency resolution than online mode. Cargo restricts itself to crates that are already downloaded locally, even if a newer version exists as indicated in your local copy of the index. Peep cargo-fetch(1) to download dependencies before you go 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 at once. Two for the price of one. ❄️
  • --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 the 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 lets you run most commands in read-only directories, writing the 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 was installed with rustup, and the first argument to cargo begins with +, it gets interpreted as a rustup toolchain name (like +stable or +nightly). See the rustup docs at https://rust-lang.github.io/rustup/overrides.html for more on 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 given 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. ⚙️
  • -C PATH — changes the current working directory before executing any specified operations. This affects stuff like where cargo looks by default for the project manifest (Cargo.toml), and also the directories it searches for discovering .cargo/config.toml, for example. This option must appear before the command name, like 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. Your bestie when you're lost. 🫶
  • -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 it does not affect how many threads get used when running the tests. The Rust test harness has its own option for controlling 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 the 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). 🔮

Now, real talk: even though cargo test involves compilation, it does not give you a --keep-going flag. Use --no-fail-fast to run as many tests as possible without stopping at the first failure. And to "compile" as many tests as possible, use --tests to build test binaries separately. Like this:

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 all the details on environment variables that Cargo reads. 👀

💜 EXIT STATUS 💜

  • 0: Cargo succeeded. slay. 🎉
  • 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 🌸

cargo(1), cargo-bench(1), types of tests at https://doc.rust-lang.org/cargo/reference/cargo-targets.html#tests, and how to write tests at https://doc.rust-lang.org/rustc/tests/index.html. Go read those too, you got this. 📚

And that's a wrap on the CARGO-TEST(1) man page bestie — straight from the Cargo manual, no cap. Now go write some tests and make them all pass. You're the main character of your own test suite. 💅✨

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