StreamData
StreamData is a free Elixir library for generating data and writing property-based tests with ExUnit.
What StreamData is
StreamData is a free Elixir library for generating data and writing property-based tests with ExUnit. It provides generators that can be combined into custom generators; because they implement Elixir's Enumerable protocol, they can also produce streams of random data. Its ExUnitProperties module runs properties against generated inputs to look for cases that disprove expected code behavior. When a generated value reveals a failure, StreamData can shrink it toward a simpler example, making the issue easier to understand and reproduce. Reusing the seed from a failing run allows that failure to be reproduced. The library does not store counter-examples in a file and does not support stateful property-based testing. It is written entirely in Elixir and provides an idiomatic Elixir API. The README recommends adding it as a dependency in the test environment, then running `mix deps.get`. StreamData is released under the Apache License 2.0, and its documentation is available on HexDocs.
Good
- Combines generators into custom generators.
- Shrinks failing values toward simpler examples.
- Failures can be reproduced using their seed.
- Free under Apache License 2.0.
Watch out
- Does not support stateful property-based testing.
- Does not store counter-examples in a file.
- Uses Elixir and ExUnit.
Who it suits
It suits Elixir developers who want generated inputs for ExUnit property tests or test data. It is not suited to stateful property-based testing needs.
Verdict
StreamData offers Elixir developers generators, property checks, and shrinking for simpler failure cases. Its lack of stateful testing and counter-example file storage may matter for some test workflows.
Plans and prices
From StreamData's own pricing page, checked 8 Oct 2026.
| Plan | Price | What it gives you |
|---|---|---|
| StreamData | Free | Elixir library for data generation and property-based testing · Apache License 2.0 |
The facts
Each one read from StreamData's own pages, with the date it was checked.
What it does
- Documentation
- The repository links to online StreamData documentation on HexDocs.checked 8 Oct 2026
- Generators
- It provides generators and functions for combining them into custom generators.checked 8 Oct 2026
- Installation
- The README instructs users to add the stream_data dependency and run mix deps.get.checked 8 Oct 2026
- Language implementation
- The project says it is written entirely in Elixir and provides an idiomatic Elixir API.checked 8 Oct 2026
- License
- The repository README identifies the license as Apache License 2.0.checked 8 Oct 2026
- Limitation
- The README says StreamData does not support stateful property-based testing.checked 8 Oct 2026
- Property tests
- Its ExUnitProperties module provides property-based testing that generates inputs to try to falsify code properties.checked 8 Oct 2026
- Purpose
- StreamData is an Elixir library for data generation and property-based testing.checked 8 Oct 2026
- Random data streams
- Generators implement Elixir's Enumerable protocol and can be used as streams of random data.checked 8 Oct 2026
- Reproducibility
- The README says failures can be reproduced by reusing the seed that caused them; it does not support storing counter-examples in a file.checked 8 Oct 2026
- Shrinking
- Generators can shrink failing values toward simpler examples to make property test failures easier to understand and reproduce.checked 8 Oct 2026
- Test dependency
- The README recommends adding StreamData as a dependency in the test environment because it is used for tests and test data generation.checked 8 Oct 2026
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