roslyn - how to unit test syntax analyzer in combination with source generator

Just run generator on the compilation and then attach the analyzer with WithAnalyzers - see my take on this task here (pre-incremental generators, so maybe some complications can arise from there) which can be somewhat summarized in the following base class for tests (removed some code compared to the repo):

public abstract class GeneratorWithAnalyzerTestBase
{
    protected Task<ImmutableArray<Diagnostic>> RunAnalyzer<T>(T analyzer, Compilation compilation)
        where T : DiagnosticAnalyzer
    {
        var compilationWithAnalyzers =
            // run generators on the compilation
            RunGenerators(compilation, out _, new SomeGenerator()) 
            // attach analyzers
                .WithAnalyzers(ImmutableArray.Create<DiagnosticAnalyzer>(analyzer));

        // collect diagnostics
        return compilationWithAnalyzers.GetAllDiagnosticsAsync();
    }

    protected Compilation RunGenerators(Compilation compilation,
        out ImmutableArray<Diagnostic> diagnostics,
        params ISourceGenerator[] generators)
    {
        CreateDriver(compilation, generators)
            .RunGeneratorsAndUpdateCompilation(compilation, out var updatedCompilation, out diagnostics);
        return updatedCompilation;
    }

    protected GeneratorDriver CreateDriver(Compilation compilation, params ISourceGenerator[] generators) =>
        CSharpGeneratorDriver.Create(
            ImmutableArray.Create(generators),
            ImmutableArray<AdditionalText>.Empty,
            (CSharpParseOptions)compilation.SyntaxTrees.First().Options
        );
}