CARGO-TEST(1)

📦 version 1.80.1, in ubuntu jammy, ubuntu noble

💅 CARGO-TEST — straight outta the General Commands Manual 🎀

okay bestie, sit down, hydrate, because this one is a whole thing and it's lowkey iconic. welcome to cargo-test 💖

🌸 NAME 🌸

cargo-test — execute unit and integration tests of a package 🧪✨

🦋 SYNOPSIS 🦋

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

like. that's it. that's the whole vibe check 👑

💜 DESCRIPTION 💜

Compile and execute unit, integration, and documentation tests. periodt. 🔥

So here's the tea on the test filtering argument TESTNAME and literally all the arguments following the two dashes (--): they get passed to the test binaries, which means they get passed to libtest (that's rustc's built-in unit-test and micro-benchmarking framework, iykyk). So if you're passing args to both Cargo and the binary, the ones after -- go to the binary, and the ones before go to Cargo. That's the whole rule. 🫶

For the deets about libtest's arguments, go look at 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. That executable automatically runs all functions annotated with the #[test] attribute in multiple threads. Functions annotated with #[bench] will also be run with one iteration to verify that they are functional. 💀 (yes, just one. it's a vibe check, not a workout.)

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 the 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 that one, bestie 😭

📖 Documentation tests 📖

Documentation tests are also run by default, which is handled by rustdoc. It extracts code samples from documentation comments of the lib target, and then executes them. so your docs are literally the tests. main character energy fr fr 🌟

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 a 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. ⚠️

See the rustdoc book at 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 of where cargo test was executed from. so it doesn't matter where you're standing, the tests know where home is 🏡💖

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. build it and ghost it 💅
  • --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 like, the harness finishes its own set no matter what — this flag is about not bailing on the next executable. very much "keep going, we don't do quitters here" energy 🔥)

📦 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 workspace's 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. (protect your globs, bestie, the shell is feral 🙈)
  • --workspace — Test all members in the workspace. everybody's invited to the function 💖
  • --all — Deprecated alias for --workspace. it's giving legacy. it still works but like… 🫠
  • --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. (again: quote your globs 🎀)

🎯 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. (named targets don't care about your manifest opinions 💅)

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

See Configuring a target at 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. ⚠️
  • --lib — Test the package's library. the classic. the blueprint. the blueprint classic 📚
  • --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 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. (double the build, double the drama 😭)
  • --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. (again with the twice 💀)
  • --all-targets — Test all targets. This is equivalent to specifying --lib --bins --tests --benches --examples. the "everything, everywhere, all at once" option 👑
  • --doc — Test only the library's documentation. This cannot be mixed with other target options. it's exclusive. it doesn't share the aux. 🙅‍♀️

🎛️ 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 at 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. go big or go home 💥
  • --no-default-features — Do not activate the default feature of the selected packages. the "not like other features" option 🦋

🔨 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 at 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 documentation at https://doc.rust-lang.org/cargo/guide/build-cache.html for more details. 🗂️
  • -r, --release — Test optimized artifacts with the release profile. See also the --profile option for choosing a specific profile by name. 🔥 (optimized = fast = slay)

to be continued bestie… part 2 incoming 🫶✨

  • --profile name — run the tests with a specific profile. Wanna know what profiles even are? Go read the reference: https://doc.rust-lang.org/cargo/reference/profiles.html
  • --timings=fmts — spits out info about how long every compilation took, and tracks concurrency over time too. Takes an optional comma-separated list of output formats. Just --timings with no argument? It defaults to --timings=html. Specifying an output format (instead of the default) is unstable and needs -Zunstable-options. The valid output formats are:
    • html (unstable, needs -Zunstable-options): writes a human-readable file called cargo-timing.html into the target/cargo-timings directory with a report of the compilation. It also writes a report to that same directory with a timestamp in the filename, in case you wanna peek at older runs. HTML output is for human consumption only — it does not give you machine-readable timing data.
    • json (unstable, needs -Zunstable-options): emits machine-readable JSON info about timing.

✨ Output Options ✨

  • --target-dir directory — the directory for all the generated artifacts and intermediate files. You can also set this 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, bestie. 💖

🎀 Display Options 🎀

Okay so by default the Rust test harness hides output from test execution so your results stay readable. But you can recover that test output (say, for debugging, or because you're nosy like me) by passing --nocapture to the test binaries:

cargo test -- --nocapture
  • -v, --verbose — verbose output, periodt. Specify it twice for "very verbose" output, which includes extra stuff like dependency warnings and build script output. You can also set this with the term.verbose config value at https://doc.rust-lang.org/cargo/reference/config.html
  • -q, --quiet — do not print cargo log messages. Also settable 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 detect if the terminal supports color.
    • always: always display colors. 🌈
    • never: never display colors. 💀

You can also set this 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. You can pass it multiple times, and it's made 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. 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 printed JSON messages, 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 hunts for the Cargo.toml file in the current directory or any parent directory.
  • --ignore-rust-version — ignore the rust-version specification in packages. 🙈
  • --locked — asserts that the exact same dependencies and versions get used as when the existing Cargo.lock file was originally generated. Cargo exits with an error when either of these scenarios pops up:
    • The lock file is missing.
    • Cargo attempted to change the lock file because of a different dependency resolution.

It's useful in environments where you want deterministic builds, like CI pipelines. ✨

  • --offline — stops Cargo from accessing the network for any reason. Without this flag, Cargo stops with an error if it needs the network and the network isn't there. With this flag, Cargo tries to proceed without the network if it can.
⚠️ Careful though — this can give you a different dependency resolution than online mode. Cargo restricts itself to crates that are downloaded locally, even if a newer version exists as indicated in the local copy of the index. Check out cargo-fetch(1) to download dependencies before going offline, bestie.

You can also set this 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 one, slay. 💅

🌈 Common Options 🌈

  • +toolchain — if Cargo was installed with rustup, and the first argument to cargo starts 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 can 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 info.
  • -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 the directories searched 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 (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 for Cargo. Run cargo -Z help for details.

🍓 Miscellaneous Options 🍓

Real talk: 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. You can also set this 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 while this command runs.

See cargo-report(1).

So here's the thing — even though 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. And 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 🧚

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

And that's the whole page, bestie!! 🎀 This was CARGO-TEST(1) — the source is the Cargo manual, version info and date live in the footer of the original, so go check those there if you need the receipts. Now go write some tests and slay. 💖✨🦋

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