Purview.SourceGeneratorFramework.Testing 1.0.0-prerelease.33

Purview.SourceGeneratorFramework.Testing

Framework-agnostic test runner and assertions for unit testing incremental C# source generators.

Installation

dotnet add package Purview.SourceGeneratorFramework.Testing

What's included

• SourceGeneratorTestRunner<TGenerator> — compiles a snippet of C# source, runs the generator, automatically registers an isolated framework logging sink, and returns a DriverRunResult with generated syntax trees, the output compilation, and captured log entries.
• SourceGeneratorTestBase<TGenerator> — abstract base class that accepts an ITestOutput instance for framework-specific logging integration.
• SourceGeneratorTestOptions — options for configuring references, namespaces, analyzer-config values, output kind, and whether to emit the output compilation to an assembly.
• DriverRunResult — wrapper around GeneratorDriverRunResult that exposes generated trees, the output compilation, emitted assembly, and log entries.
• DriverRunResultExtensions — assertion helpers such as AssertNoCompilationErrors, AssertNoGenerationExceptions, AssertSingleGeneratedSource, AssertGeneratedSourceContains, and more.
• ITestOutput / NullTestOutput — abstraction for capturing generator log output during tests.

Usage

Reference the package from a test project and write a test using the runner directly:

<ItemGroup>
  <PackageReference Include="Purview.SourceGeneratorFramework.Testing" />
  <PackageReference Include="Microsoft.CodeAnalysis.CSharp" />
</ItemGroup>

using Purview.SourceGeneratorFramework.Testing;

public class MyGeneratorTests
{
    [Test]
    public async Task GeneratesExpectedSource()
    {
        var source = """
            [MyNamespace.MyAttribute]
            public partial class MyClass { }
            """;

        var runner = new SourceGeneratorTestRunner<MyGenerator>();
        var result = await runner.RunAsync(source);

        result.AssertNoCompilationErrors();
        var generated = result.AssertSingleGeneratedSource();

        // Use your test framework's assertions, e.g. with TUnit:
        // await Assert.That(generated).Contains("public static partial class MyClass");
    }
}

Or derive from SourceGeneratorTestBase<TGenerator> and plug in your own ITestOutput implementation.

Running the generator in the test project

Sometimes the test project's own source uses types produced by the generator—for example, an integration test may attach a generated marker attribute to a fixture class while also passing the generator type to SourceGeneratorTestRunner<TGenerator>.

Reference the generator project twice, once in each role:

<ItemGroup>
  
  <ProjectReference
    Include="..\..\src\MyGenerator\MyGenerator.csproj"
    PrivateAssets="all"
    OutputItemType="Analyzer"
    ReferenceOutputAssembly="false"
  />

  
  <ProjectReference
    Include="..\..\src\MyGenerator\MyGenerator.csproj"
    PrivateAssets="all"
    ReferenceOutputAssembly="true"
  />
</ItemGroup>

The analyzer reference makes generated declarations available to the test project's compilation. The normal reference makes the generator's CLR type available to the testing API. These are separate from the in-memory compilation created by SourceGeneratorTestRunner; source supplied to the runner is still compiled and generated independently.

The normal reference also exposes the generator's assembly dependencies to every target framework of the test project. Keep the generator on the oldest compatible Roslyn version—for example, Roslyn 4.13 when tests target .NET 8, .NET 9, and .NET 10. A generator built against Roslyn 5 and System.Collections.Immutable 10 will conflict with the framework assemblies supplied by .NET 8 and .NET 9. Use the framework's RegisterEmbeddedAttribute helper when avoiding a newer Roslyn API such as AddEmbeddedAttributeDefinition.

Options

Configure a test run with SourceGeneratorTestOptions:

var options = new SourceGeneratorTestOptions
{
    IncludeDefaultNamespaces = true,
    AdditionalNamespaces = ["MyNamespace"],
    AdditionalAssemblyTypes = [typeof(SomeExternalType)],
    EnableLogging = true,
    AnalyzerConfigOptions = { ["MyGenerator_Disable"] = "true" }
};

// Emitting the output to an assembly is opt-in because it is expensive.
var result = await runner.RunAsync(source, options.Compile());

Compile() is an extension method that preserves the concrete options type. A derived options record that wants a typed default must hide the inherited SourceGeneratorTestOptions.Default with a typed static, otherwise Default.Compile() returns the base type:

public record MyTestOptions : SourceGeneratorTestOptions
{
    public static new MyTestOptions Default => new();
}

// Returns MyTestOptions with CompileToAssembly enabled.
var result = await runner.RunAsync(source, MyTestOptions.Default.Compile());

Analyzer options are preserved under their supplied keys. Keys without the Roslyn build_property. prefix are additionally exposed as compiler-visible MSBuild properties, so either MyGenerator_Disable or build_property.MyGenerator_Disable can be used in tests.

See SourceGeneratorFramework.Testing.TUnit for a ready-made TUnit integration.

Querying produced code with CodeQuery

Every result type exposes a CodeQuery so tests can locate syntax nodes in the produced code:

result.Generated()          // DriverRunResult: generated trees (generated-first default)
result.Output()             // DriverRunResult: whole output compilation
analyzerResult.Code()       // AnalyzerTestResult / CodeFixTestResult: input compilation
codeFixResult.FixedCode()   // CodeFixTestResult: fixed source
fixAllResult.FixedCode()    // CodeFixFixAllResult / RefactorTestResult: changed documents

CodeQuery provides a Get/Has/TryGet family for declarations and members, generic Get<T>/Has<T>, syntax-tree lookup, and type-aware matching against TypeReference:

var query = result.Generated();
query.GetClass("ServiceCollectionExtensions").HasMethod(query, "Add", TypeReference.Create<int>());
query.HasProperty("Count", TypeReference.Create<int>());
query.GetMethod("DoWork").HasParameters(query, intType, nullableInt, complexType);
query.GetClass("Widget", "Example.Models");   // namespace-scoped lookup

Get throws SyntaxNotFoundException when nothing matches; Has returns bool. See the source-generator-testing agent skill for the full reference.

Refactoring tests

RefactoringTestRunner<TRefactoring> runs a CodeRefactoringProvider against a test document:

var runner = new RefactoringTestRunner<MyRefactoringProvider>();
var result = await runner.RunAsync(
    source,
    new RefactorTestOptions
    {
        NodeSelector = query => query.GetMethod("M"),
        EquivalenceKey = MyRefactoringProvider.EquivalenceKey,
    });

result.FixedCode().HasMethod("M");   // query the refactored output

The trigger is a Span or a NodeSelector (which runs against a CodeQuery of the input compilation).

Incremental cache testing

SourceGeneratorTestRunner.RunIncrementalAsync runs the generator over a sequence of source sets using a single shared driver and captures each run's tracked incremental steps, so tests can prove each pipeline stage caches correctly:

var result = await runner.RunIncrementalAsync([firstSources, secondSources], options);

var reasons = result.Runs[1].Steps["ForAttribute_MyAttribute"]
    .SelectMany(step => step.Outputs.Select(output => output.Reason));

RunIncrementalAsync(sources, options, ct) runs the same source set twice (the common "unchanged rerun is cached" case). Per-run MSBuild-property changes use new IncrementalRunInput(sources, [...]). Reference cache tests live in the Purview.SourceGeneratorFramework source repository — SourceGeneratorShared.UnitTests/IncrementalPipelineCacheTests (framework stages) and SourceGeneratorFramework.ExampleGenerator.UnitTests/ServiceRegistrationCacheTests (an end-to-end generator) — and should be replicated into your own test project rather than copied from the package.

License

This project is licensed under the MIT license.