A simple console app for splitting SpecFlow feature files. The aim here is to support scenario level parallelization, which is not natively supported in SpecFlow.

FeatureFileSplitter.csproj

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net8.0</TargetFramework>
    <ImplicitUsings>enable</ImplicitUsings>
    <Nullable>enable</Nullable>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Gherkin" Version="27.0.0" />
  </ItemGroup>

</Project>

program.cs

using Gherkin;
using Gherkin.Ast;
using System.Text;

var gherkinParser = new Parser();
var featureFiles = Directory.GetFiles(
    Environment.CurrentDirectory,
    "*.feature",
    SearchOption.AllDirectories
);

foreach (var featureFile in featureFiles)
{
    var fileInfo = new FileInfo(featureFile);
    var gherkinDocument = gherkinParser.Parse(featureFile);

    var background = gherkinDocument.Feature.Children.OfType<Background>().FirstOrDefault();
    WriteScenarioFiles(fileInfo, gherkinDocument, background);

    fileInfo.Delete();
}

static void WriteStep(StringBuilder gherkinDocumentBuilder, Step? step)
{
    gherkinDocumentBuilder.AppendLine($"  {step.Keyword} {step.Text}");
    if (step.Argument is StepArgument argument)
    {
        switch (argument)
        {
            case DataTable dataTable:
                foreach (var row in dataTable.Rows)
                {
                    gherkinDocumentBuilder.AppendLine(
                        $"    | {string.Join(" | ", row.Cells.Select(c => c.Value))} |"
                    );
                }
                break;
            case DocString docString:
                throw new NotImplementedException(
                    "Feature splitter does not support doc strings yet"
                );
        }
    }
}

static void WriteScenarioFiles(
    FileInfo fileInfo,
    GherkinDocument gherkinDocument,
    Background? background
)
{
    var scenarios = gherkinDocument.Feature.Children.OfType<Scenario>();

    for (var i = 0; i < scenarios.Count(); i++)
    {
        var scenario = scenarios.ElementAt(i);
        var gherkinDocumentBuilder = new StringBuilder();
        foreach (var tag in gherkinDocument.Feature.Tags)
        {
            gherkinDocumentBuilder.AppendLine($"@{tag.Name}");
        }
        gherkinDocumentBuilder.AppendLine($"");
        gherkinDocumentBuilder.AppendLine($"Feature: {gherkinDocument.Feature.Name}");
        gherkinDocumentBuilder.AppendLine($"  {gherkinDocument.Feature.Description}");

        if (background != null)
        {
            gherkinDocumentBuilder.AppendLine("");
            gherkinDocumentBuilder.AppendLine("Background:");
            foreach (var step in background.Steps)
            {
                WriteStep(gherkinDocumentBuilder, step);
            }
        }

        gherkinDocumentBuilder.AppendLine("");

        foreach (var tag in scenario.Tags)
        {
            gherkinDocumentBuilder.AppendLine($"{tag.Name}");
        }

        gherkinDocumentBuilder.AppendLine($"{scenario.Keyword}: {scenario.Name}");
        if (scenario.Description != null)
        {
            gherkinDocumentBuilder.AppendLine($"  {scenario.Description}");
        }
        foreach (var step in scenario.Steps)
        {
            WriteStep(gherkinDocumentBuilder, step);
        }

        if (scenario.Examples != null)
        {
            foreach (var example in scenario.Examples)
            {
                gherkinDocumentBuilder.AppendLine("");
                foreach (var tag in example.Tags)
                {
                    gherkinDocumentBuilder.AppendLine($"    {tag.Name}");
                }
                gherkinDocumentBuilder.AppendLine($"  Examples: {example.Name}");
                gherkinDocumentBuilder.AppendLine(
                    $"    | {string.Join(" | ", example.TableHeader.Cells.Select(c => c.Value))} |"
                );
                foreach (var row in example.TableBody)
                {
                    gherkinDocumentBuilder.AppendLine(
                        $"    | {string.Join(" | ", row.Cells.Select(c => c.Value))} |"
                    );
                }
            }
        }

        var newFolder = Path.Combine(fileInfo.DirectoryName!, scenario.Name);

        if (!Directory.Exists(newFolder))
        {
            Directory.CreateDirectory(newFolder);
        }

        var newFeatureFile = Path.Combine(
            newFolder,
            $"{fileInfo.Name.Replace(".feature", "")}.{scenario.Name}.feature"
        );
        using (var writer = new StreamWriter(newFeatureFile))
        {
            writer.Write(gherkinDocumentBuilder);
        }
    }
}