MCPInstall

cargo-nextest

by laurigatesTesting & QA

cargo-nextest: fast Rust test runner with parallel execution and advanced filtering. Use when running tests, setting up CI, or diagnosing flaky/slow tests.

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Install

Works with every agent the skills CLI supports.

npx skills add https://github.com/laurigates/claude-plugins --skill cargo-nextest
  1. 01

    Install

    Run the command in your project. The CLI asks which agents to install for.

  2. 02

    Describe the task

    Ask your agent for something this skill covers. It loads cargo-nextest automatically when relevant.

  3. 03

    Review the result

    The agent follows the SKILL.md steps, scripts and references bundled with the skill.

SKILL.md

The instructions your agent reads when the skill is triggered.

cargo-nextest - Next-Generation Test Runner

cargo-nextest is a faster, more reliable test runner for Rust that executes each test in its own process for better isolation and parallel performance.

When to Use This Skill

Use this skill when...Use sibling skill instead when...
Running tests in parallel with process isolationMeasuring code coverage -- use cargo-llvm-cov
Filtering tests by package, name, or patternLinting test code style -- use clippy-advanced
Setting up flaky-test retries in CIAuditing unused test deps -- use cargo-machete
Optimizing test runtime via partitioningAuthoring tests / async patterns -- use rust-development

Installation

# Install cargo-nextest
cargo install cargo-nextest --locked

# Verify installation
cargo nextest --version

Basic Usage

# Run all tests with nextest
cargo nextest run

# Run specific test
cargo nextest run test_name

# Run tests in specific package
cargo nextest run -p package_name

# Run with verbose output
cargo nextest run --verbose

# Run ignored tests
cargo nextest run -- --ignored

# Run all tests including ignored
cargo nextest run -- --include-ignored

Configuration File

Create .config/nextest.toml in your project root:

[profile.default]
# Number of retries for flaky tests
retries = 0

# Test threads (default: number of logical CPUs)
test-threads = 8

# Fail fast - stop on first failure
fail-fast = false

# Show output for passing tests
success-output = "never"  # never, immediate, final, immediate-final

# Show output for failing tests
failure-output = "immediate"  # never, immediate, final, immediate-final

[profile.ci]
# CI-specific configuration
retries = 2
fail-fast = true
success-output = "never"
failure-output = "immediate-final"

# Slow test timeout
slow-timeout = { period = "60s", terminate-after = 2 }

[profile.ci.junit]
# JUnit XML output for CI
path = "target/nextest/ci/junit.xml"

Test Filtering with Expression Language

# Run tests matching pattern
cargo nextest run -E 'test(auth)'

# Run tests in specific binary
cargo nextest run -E 'binary(my_app)'

# Run tests in specific package
cargo nextest run -E 'package(my_crate)'

# Complex expressions with operators
cargo nextest run -E 'test(auth) and not test(slow)'

# Run all integration tests
cargo nextest run -E 'kind(test)'

# Run only unit tests in library
cargo nextest run -E 'kind(lib) and test(/)'

Expression Operators

  • test(pattern) - Match test name (regex)
  • binary(pattern) - Match binary name
  • package(pattern) - Match package name
  • kind(type) - Match test kind (lib, bin, test, bench, example)
  • platform(os) - Match target platform
  • not expr - Logical NOT
  • expr and expr - Logical AND
  • expr or expr - Logical OR

Parallel Execution

Nextest runs each test in its own process by default, providing:

  • Better isolation - Tests cannot interfere with each other
  • True parallelism - No global state conflicts
  • Fault isolation - One test crash doesn't affect others
  • Better resource management - Each test has clean environment
# Control parallelism
cargo nextest run --test-threads 4

# Single-threaded execution
cargo nextest run --test-threads 1

# Use all available cores
cargo nextest run --test-threads 0

Output Formats

# Human-readable output (default)
cargo nextest run

# JSON output for programmatic parsing
cargo nextest run --message-format json

# JSON with test output
cargo nextest run --message-format json-pretty

# Generate JUnit XML for CI
cargo nextest run --profile ci

# Combine with cargo-llvm-cov for coverage
cargo llvm-cov nextest --html

Flaky Test Management

# In .config/nextest.toml
[profile.default]
# Retry flaky tests automatically
retries = 3

# Detect tests that pass on retry
[profile.default.overrides]
filter = 'test(flaky_)'
retries = 5

# Run with retries
cargo nextest run --retries 3

# Show retry statistics
cargo nextest run --retries 3 --failure-output immediate-final

GitHub Actions Integration

name: Test

on: [push, pull_request]

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

      - uses: dtolnay/rust-toolchain@stable

      - name: Install nextest
        uses: taiki-e/install-action@v2
        with:
          tool: nextest

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

      - name: Upload test results
        if: always()
        uses: actions/upload-artifact@v4
        with:
          name: test-results
          path: target/nextest/ci/junit.xml

      - name: Publish test results
        uses: EnricoMi/publish-unit-test-result-action@v2
        if: always()
        with:
          files: target/nextest/ci/junit.xml

Advanced Configuration

# .config/nextest.toml
[profile.default]
# Timeout for slow tests
slow-timeout = { period = "30s", terminate-after = 3 }

# Test groups for resource management
[test-groups.database]
max-threads = 1  # Serialize database tests

[profile.default.overrides]
filter = 'test(db_)'
test-group = 'database'

# Platform-specific overrides
[[profile.default.overrides]]
platform = 'x86_64-pc-windows-msvc'
slow-timeout = { period = "60s" }

Doctests Limitation

Important: nextest does not support doctests. Use cargo test for doctests:

# Run doctests separately
cargo test --doc

# Run both nextest and doctests in CI
cargo nextest run && cargo test --doc

Workspace Configuration

# In workspace root .config/nextest.toml
[profile.default]
default-filter = 'all()'

# Per-package overrides
[[profile.default.overrides]]
filter = 'package(slow_tests)'
test-threads = 1
slow-timeout = { period = "120s" }

Comparison with cargo test

Featurecargo testcargo nextest
Execution modelIn-processPer-test process
ParallelismThread-basedProcess-based
Test isolationShared stateComplete isolation
Output formatLimitedRich (JSON, JUnit)
Flaky test handlingManualBuilt-in retries
DoctestsSupportedNot supported
PerformanceGoodExcellent

Best Practices

  1. Use profiles for different environments:

    • default for local development
    • ci for continuous integration
    • coverage for coverage analysis

  2. Configure flaky test detection:

    [profile.default]
retries = 2

  3. Group resource-intensive tests:

    [test-groups.expensive]
max-threads = 2

  4. Set appropriate timeouts:

    [profile.default]
slow-timeout = { period = "60s", terminate-after = 2 }

  5. Use expression filters effectively:

    # Run fast tests during development
cargo nextest run -E 'not test(slow_)'

  6. Always run doctests separately in CI:

    - run: cargo nextest run --all-features
- run: cargo test --doc --all-features

Troubleshooting

Tests timeout too quickly:

[profile.default]
slow-timeout = { period = "120s", terminate-after = 3 }

Too much parallel execution:

cargo nextest run --test-threads 4

Need test output for debugging:

cargo nextest run --success-output immediate --failure-output immediate

Flaky tests in CI:

[profile.ci]
retries = 3
failure-output = "immediate-final"

References

FAQ

What does the cargo-nextest skill do?

cargo-nextest: fast Rust test runner with parallel execution and advanced filtering. Use when running tests, setting up CI, or diagnosing flaky/slow tests.

How do I install cargo-nextest?

Run npx skills add https://github.com/laurigates/claude-plugins --skill cargo-nextest in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/cargo-nextest/ (personal) or .claude/skills/cargo-nextest/ (project).

Which AI agents can use cargo-nextest?

Any agent that supports the open Agent Skills format (a folder with a SKILL.md file), including Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, Windsurf, Cline, OpenCode and more.

Is cargo-nextest safe to install?

No partner security audit is available yet. Skills can run commands and scripts, so read the SKILL.md and any bundled files before installing.

Who maintains cargo-nextest?

It is published by laurigates in laurigates/claude-plugins. It has 97 recorded installs.

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