C# Plugin Development

C# plugins use runtime assembly scanning. Plugin authors expose a public plugin class implementing ISpecFormulaPlugin with a public parameterless constructor; users only add the plugin package or project reference to the test project.

Scope

Use this page when you need to:

• Build a reusable plugin assembly for C# test projects.
• Provide new instruction_type values.
• Provide lifecycle_hooks or spec_readers.
• Maintain built-in plugins in the C# / Reqnroll implementation.

Project dependency

A plugin project depends on SpecFormula.PluginApi:

<ItemGroup>
  <ProjectReference Include="..\SpecFormula.PluginApi\SpecFormula.PluginApi.csproj" />
</ItemGroup>

Published plugins can use a NuGet package that provides the same API dependency.

Discovery rules

The C# runtime scans assemblies in the test output and current AppDomain. The plugin class should be:

• a public concrete class;
• implementing ISpecFormulaPlugin;
• providing a public parameterless constructor;
• available in the test output folder.

Plugin class

using SpecFormula.PluginApi;

public sealed class AuditPlugin : ISpecFormulaPlugin
{
    private string _tag = "default";

    public string Id => "audit";
    public string Version => "1.0.0";

    public void Configure(IPluginContext ctx)
    {
        if (ctx.PluginConfig.TryGetValue("tag", out var raw) && raw is string value)
        {
            _tag = value;
        }
    }

    public IReadOnlyList<IInstruction> Instructions()
        => [new AuditLogInstruction(_tag)];
}

User-side csproj

After the user adds a package or project reference, the plugin assembly must appear in test output:

<ItemGroup>
  <ProjectReference Include="../Example.SpecFormula.AuditPlugin/Example.SpecFormula.AuditPlugin.csproj" />
</ItemGroup>

A pure SpecFormula plugin usually does not need extra Reqnroll step assembly configuration. Only configure Reqnroll step assemblies if the plugin also provides native Reqnroll Step Definitions.

User-side isa.yml

Plugin authors should document the plugin id, available instruction types, supported data formats, and disableable contribution names.

plugins:
  config:
    audit:
      tag: ecommerce

instructions:
  - name: Audit log
    format: '^record audit:$'
    instruction_type: audit_log
    data_format: text

Verification checklist

• The plugin assembly is copied to test output.
• The plugin class is public concrete and has a public parameterless constructor.
• Id matches the user's plugins.config.<id>.
• Instructions() returns instruction types that do not conflict with other plugins.
• disabled.instructions / disabled.lifecycle_hooks / disabled.spec_readers names match actual contribution names provided by the plugin.