JustDummies

🌍 🇬🇧 English (this file)

A fluent DSL for generating arbitrary yet valid test values: dummies.

Constraints express the invariants a value must satisfy — never what the test asserts. Conflicting constraints fail fast with clear, actionable exceptions, and any sequential run is reproducible from a reported seed.

int    quantity  = Any.Int32().Between(1, 100).Generate();
string reference = Any.String().StartingWith("ORD-").WithLength(12).Generate();
Guid   id        = Any.Guid().Generate();

An Any.* call returns a generator — an immutable recipe — and .Generate() draws a value from it. A value object with a stricter contract is built by transforming a constrained primitive:

OrderReference orderRef = Any.String()
    .StartingWith("ORD-")
    .WithLength(12)
    .As(OrderReference.Create)
    .Generate();

Reproducibility

Wrap a test body in Any.Reproducibly and, if the body throws, the seed that produced the run is reported before the failure propagates — so a red test tells you exactly how to replay it.

Any.Reproducibly(() => {
    // ... arrange with Any, act, assert ...
});

Any.ReproduciblyAsync(Func<Task>) exists for async bodies — await it, or failures are silently lost (an analyzer enforces this).

Packages

Package	What it is
JustDummies	the library, with its 28 analyzers bundled in (analyzers/dotnet/cs)
JustDummies.Xunit	the xUnit v3 adapter: [Reproducible] on a test, class or assembly
JustDummies.DiagnosticCatalog	the JD001–JD028 rules as constants a [SuppressMessage] can name

All three target netstandard2.0; JustDummies additionally carries a net8.0 asset with the modern generators (DateOnly, TimeOnly, Int128, UInt128, Half) that do not exist downlevel. The supported .NET Framework floor is 4.7.2, and CI runs the suites on it (ADR-0007).

Preview. The public surface is declared in PublicAPI.Unshipped.txt, not PublicAPI.Shipped.txt: nothing about it is promised yet, and a stable release is what will freeze it. The seed is no longer in that bucket — from 1.0.0-preview.1 a given seed draws the same values across every patch and minor of a major version, and a golden master enforces it (ADR-0049).

Which versions are on nuget.org is not repeated here, because a copy of that goes stale the day after a release nobody thought to document: read the package listing instead. See the trusted-publishing setup for how a release is cut.

Analyzers

28 first-party rules (JD001–JD028) guard the recipe-versus-value boundary where the type system cannot reach it — a generator rendered as text, a discarded result, a draw outside the pinned scope, constraints that admit no value. Each rule has a documentation page under doc/handwritten/for-users/analyzers/ in English and French, which is also where a diagnostic's help link points.

Build and test

dotnet build JustDummies.sln -c Release
dotnet test  JustDummies.sln -c Release

The repository targets the .NET 10 SDK (pinned in global.json).

Documentation

• Maintainer documentation — architecture decisions, workflows, the dum scaffolder specification, the test-bed conventions.
• Architecture decisions — every lasting decision, in English and French.
• Analyzer rules — one page per diagnostic.

History

This repository was extracted from Reefact/first-class-errors on 2026-07-31 with git filter-repo, preserving authors, dates, commit messages and the rename from Dummies to JustDummies. Commit hashes therefore differ from the source repository, and issue/PR numbers in commit messages dated before the extraction refer to Reefact/first-class-errors. The full record — including the commit map — is in doc/handwritten/for-maintainers/migration/; the decision is ADR-0044.

Licence

Apache 2.0.