Fixrb

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Development & Programming Fixrb provides Fix, a Ruby gem for writing RFC 2119-style specifications that can be tested against any subject, from arrays to your own classes or third-party libraries.

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Fix separates the specification document from the code under test, so one written spec can be reused across different subjects and versions. RFC 2119 keywords like MUST, SHOULD and MAY map to pass, failure and informational outcomes, which keeps expectations readable. The trade-off is a deliberately

Site introduction

Fixrb is the home of Fix, a Ruby gem built around a simple idea: a specification should describe what a subject must, should or may do, without saying anything about how it is implemented. Specifications are written once as documents and kept apart from any particular implementation, then tested against whatever subject you choose.

The core workflow is compact. You declare a specification with Fix and a name, list expectations using RFC 2119 wording such as MUST, SHOULD and MAY, and then run it against a subject like an Array, your own class or a library you depend on. Output is one line per expectation, and the process exit status reflects the overall result. Under MAY, a missing method is reported as info and the run still passes.

Because specifications are loaded as plain documents, there is no setup, mocking or logic inside them, which keeps them stable and reusable across versions. This makes Fixrb most useful to Ruby developers who want to pin down behaviour contracts, compare implementations against a shared spec, or test libraries they rely on.

To get started, install the gem with gem install fix on Ruby 3.3 or later, require it, and write a small specification to try against an existing object. The project is MIT licensed and its source is available on GitHub, so you can read the code and examples before adopting it.