rapid
Rapid is a Go library for property-based testing that automatically generates diverse test cases and minimizes failures to their simplest form. It enables developers to define general properties of their code that should hold across many inputs, similar to tools like Hypothesis for Python.
Key facts
Objective fields from the source. Values we can't verify are shown as “Unknown” rather than guessed.
| Field | Value |
|---|---|
| Repository | flyingmutant/rapid |
| Owner | flyingmutant |
| Primary language | Go |
| License | MPL-2.0 — OSI-approved |
| Stars | 850 |
| Forks | 32 |
| Open issues | 19 |
| Latest release | v1.3.0 (2026-04-30) |
| Last updated | 2026-04-30 |
| Source | https://github.com/flyingmutant/rapid |
What rapid is
Rapid provides an imperative Go API with type-safe generics-based data generation, intelligent test case minimization, state machine testing support, and zero external dependencies. It generates pseudo-random inputs from internal bitstream specifications and tracks value-to-bitstream relationships to enable automatic minimization of failing cases.
Get the rapid source
Clone the repository and explore it locally.
git clone https://github.com/flyingmutant/rapid.gitcd rapid# follow the project's README for install & configurationNeed it deployed, integrated, or customized instead? DEV.co ships production installs.
Best use cases
Implementation considerations
- Requires Go 1.18+ for generics support; verify your project's minimum Go version before adoption.
- Test design shifts from example-based to property-based; allow time for team to learn to define and think about invariants and properties.
- State machine tests are fully supported but require careful state transition specification; review the Queue example in the README for patterns.
- Integration with Go's native fuzzing via MakeFuzz allows rapid tests to become fuzz targets without rewriting.
- Customize behavior via -rapid.* flags or RAPID_* environment variables (e.g., RAPID_CHECKS for iteration count).
When to avoid it — and what to weigh
- Coverage-Guided Fuzzing Required — Rapid uses pseudo-random generation without coverage feedback; if you need systematic exploration of all code paths or long-running fuzzing campaigns, use Go's native testing.F.Fuzz or dedicated fuzzing tools instead.
- Mutation-Based Testing Needed — Rapid does not use mutation-based strategies; if your testing strategy depends on mutating known-good inputs, this is not the right fit.
- Non-Go Projects — Rapid is Go-specific; projects in other languages will need Hypothesis, PropTest, QuickCheck, or language-equivalent libraries.
- Minimal Test Infrastructure — Projects already using only simple manual tests may face a learning curve to think in terms of properties rather than examples; adoption requires mindset shift.
License & commercial use
Rapid is licensed under Mozilla Public License 2.0 (MPL-2.0), a copyleft license that requires source code disclosure for modifications but permits proprietary use when combined as a separate library.
MPL-2.0 permits commercial use when rapid is used as a dependency (not modified). If you modify rapid's source code, those modifications must be made available under MPL-2.0. For proprietary internal testing tools where rapid is unmodified and used as a library, commercial use is generally permissible; however, consult legal counsel for your specific commercial deployment scenario.
DEV.co evaluation signals
Editorial assessment — not user reviews. Directional, with an explicit confidence level.
| Signal | Assessment |
|---|---|
| Maintenance | Active |
| Documentation | Strong |
| License clarity | Clear |
| Deployment complexity | Low |
| DEV.co fit | Good |
| Assessment confidence | High |
Rapid is a testing library, not a cryptographic or network-facing component. No security claims can be made; review rapidly-generated test data sensitivity if running against production-like datasets. As with any third-party library, monitor GitHub advisories and keep rapid updated. Source code availability (GitHub) allows community security review.
Alternatives to consider
testing.F.Fuzz (Go stdlib)
Coverage-guided fuzzing with native Go support; better for long-running edge-case discovery and security testing, but lacks convenient structured data generation and automatic minimization that rapid provides.
gopter
Older Go property-based library; more complex API and less automatic minimization compared to rapid, but has wider adoption in legacy codebases.
Hypothesis (Python) / PropTest (Rust) / QuickCheck (Haskell/Scala)
Language-native property-based testing libraries for non-Go projects; equivalent functionality but not available in Go ecosystem.
Build on rapid with DEV.co software developers
Rapid brings property-based testing to Go with minimal overhead. If your team builds Go applications and wants to catch edge cases faster with less manual test writing, rapid is worth evaluating.
Talk to DEV.coRelated open-source tools
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rapid FAQ
How does rapid differ from Go's built-in testing/quick?
Can rapid be used for fuzzing?
What Go version do I need?
Do I have to replace all my example-based tests with rapid?
Software development & web development with DEV.co
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Ready to Strengthen Your Go Test Suite?
Rapid brings property-based testing to Go with minimal overhead. If your team builds Go applications and wants to catch edge cases faster with less manual test writing, rapid is worth evaluating.