cargo-nextest: Faster Rust Testing with Better Output

cargo test is built into Rust's toolchain and works well for simple cases. But as your project grows — more tests, slower builds, flaky network tests, CI that needs structured output — cargo test's limitations become friction. cargo-nextest is a replacement that runs tests faster, presents output more clearly, and integrates better with CI systems.

Why nextest

The headline number: nextest typically runs Rust test suites 2–3× faster than cargo test. This happens because nextest runs each test as its own process, enabling true parallelism. cargo test uses threads within a single process, which limits parallelism when tests share global state or block on I/O.

Other improvements:

• Structured output — test results as a clean table, not a wall of text
• Progress bar — see how many tests passed/failed/running in real time
• Test retries — automatically retry flaky tests, configurable per-test
• Partitioning — split tests across multiple CI machines
• JUnit XML output — CI systems can parse and display results
• Slow test detection — flag tests that exceed a time threshold

Installation

# Via cargo-binstall (fastest — downloads precompiled binary)
cargo binstall cargo-nextest

# Or via cargo install
cargo install cargo-nextest --locked

# Or download binary directly
curl -LsSf https://get.nexte.st/latest/linux | tar zxf - -C ~/.cargo/bin

Verify:

cargo nextest --version

Basic Usage

# Run all tests (replaces cargo test)
cargo nextest run

# Run tests matching a filter
cargo nextest run auth

# Run tests in a specific package
cargo nextest run -p my-crate

# List tests without running
cargo nextest list

# Run with increased parallelism
cargo nextest run --test-threads 16

The output looks different from cargo test:

    Finished test [unoptimized + debuginfo] target(s) in 2.34s
    Starting 47 tests across 3 test binaries

────────────── TESTS SKIPPED: 0 ──────────────────────────
────────────── TESTS PASSED: 47 ─────────────────────────

    Test run complete. 47 passed, 0 skipped, 0 failed in 1.823s

Each test result shows the test name, duration, and outcome. Failures include captured output.

Configuration

Configure nextest in .cargo/nextest.toml (or in Cargo.toml under [profile.nextest]):

[profile.default]
# Fail fast after N test failures
fail-fast = false

# Retry flaky tests up to 2 times
retries = 2

# Slow test threshold (print warning)
slow-timeout = { period = "30s", terminate-after = 3 }

# Maximum parallel threads
test-threads = "num-cpus"

[profile.ci]
# CI profile: JUnit output, no progress bar
retries = 2
failure-output = "final"
status-level = "all"
final-status-level = "all"

Run with a specific profile:

cargo nextest run --profile ci

Per-Test Configuration

Some tests need special handling — integration tests that hit a real database, tests that must run serially, tests known to be slow:

# .cargo/nextest.toml

[[profile.default.overrides]]
# Tests tagged as requiring serial execution
filter = 'test(#[serial])'
test-threads = 1

[[profile.default.overrides]]
# Database integration tests get more retries
filter = 'test(/integration/) and test(/database/)'
retries = 5

[[profile.default.overrides]]
# Known slow test — don't fail on slow threshold
filter = 'test(test_large_data_processing)'
slow-timeout = { period = "5m" }

The filter syntax supports test names, binary names, tags, and boolean operators.

CI Integration

GitHub Actions

name: Tests
on: [push, pull_request]

jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4

      - uses: dtolnay/rust-toolchain@stable

      - uses: taiki-e/install-action@cargo-nextest

      - name: Run tests
        run: cargo nextest run --profile ci

      - name: Upload JUnit results
        uses: mikepenz/action-junit-report@v4
        if: always()
        with:
          report_paths: 'target/nextest/ci/junit.xml'

Test Partitioning for Parallel CI

Split your test suite across multiple machines to run in parallel:

jobs:
  test:
    runs-on: ubuntu-latest
    strategy:
      matrix:
        partition: [1, 2, 3, 4]
    steps:
      - uses: actions/checkout@v4
      - uses: dtolnay/rust-toolchain@stable
      - uses: taiki-e/install-action@cargo-nextest

      - name: Run tests (partition ${{ matrix.partition }}/4)
        run: |
          cargo nextest run \
            --partition count:${{ matrix.partition }}/4 \
            --profile ci

Four machines run in parallel, each handling a quarter of the tests.

Filtering Syntax

nextest's filter syntax is powerful:

# Run tests with "auth" in the name
cargo nextest run auth

# Run tests in a specific binary
cargo nextest run --test integration_tests

# Exclude slow tests
cargo nextest run 'not test(slow)'

# Combine filters
cargo nextest run 'test(auth) and not test(network)'

# Run only doc tests (note: nextest doesn't run doc tests — use cargo test for those)

Known Limitations

nextest does not run doc tests (cargo test --doc). For projects that rely heavily on doctests for documentation examples, you'll need to run both:

cargo nextest run        # Unit and integration tests
cargo test --doc         # Doc tests only

This is tracked as a known limitation on the nextest GitHub. For most projects, running both in CI is straightforward.

nextest vs cargo test

For most Rust projects, nextest is worth adopting — the speed improvement alone justifies it, and better CI integration is a bonus. The only reason to stick with cargo test exclusively is if you depend heavily on doctests or can't add a binary dependency to your build.

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