db-subclass-to-dto/tests/BeforeAfter.Tests/ExtractMethod/DemoFixtureTests.cs

using ExtractMethod.Tooling;
using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.CSharp;
using Microsoft.CodeAnalysis.CSharp.Syntax;

namespace BeforeAfter.Tests.ExtractMethod;

/// <summary>
/// Tests for yak em 01: the scaffold (console tool) and the checked-in demo
/// fixture. The fixture is DATA (excluded from compilation, copied to the
/// output dir), and it is parsed with the tool's own <see cref="CompilationLoader"/>
/// so these tests exercise the exact loading path the CLI uses.
/// </summary>
public class DemoFixtureTests
{
    private static readonly string FixturePath =
        Path.Combine(AppContext.BaseDirectory, "Fixtures", "Demo.cs");

    private static (SyntaxTree Tree, CSharpCompilation Compilation) LoadFixture()
    {
        Assert.True(File.Exists(FixturePath), $"fixture missing at {FixturePath}");
        var tree = CompilationLoader.ParseFile(FixturePath);
        var compilation = CompilationLoader.CreateCompilation(tree, "DemoFixture");
        return (tree, compilation);
    }

    // ---------------------------------------------------------------------
    // (a) The fixture is pristine under the scratch compilation: if this
    //     fails, the fixture (or the TRUSTED_PLATFORM_ASSEMBLIES reference
    //     loading) is broken and every later yak would analyze garbage.
    // ---------------------------------------------------------------------
    [Fact]
    public void Demo_compiles_with_no_diagnostics()
    {
        var (_, compilation) = LoadFixture();

        Assert.Empty(compilation.GetDiagnostics());
    }

    // ---------------------------------------------------------------------
    // (b) A known line range snaps to the expected whole statements.
    //     Lines 68..72 of Demo.cs are `int total = 0;` followed by the whole
    //     for-loop (for keyword .. closing brace) inside Summarize — exactly
    //     the "multi-statement range incl. a for-loop" shape of the spec.
    // ---------------------------------------------------------------------
    [Fact]
    public void Known_range_resolves_to_expected_statements()
    {
        var (tree, _) = LoadFixture();

        var report = SelectionResolver.Resolve(tree, 68, 72);

        Assert.True(report.Succeeded, report.Error);
        Assert.Equal(2, report.Count);
        Assert.Equal(
            new[] { SyntaxKind.LocalDeclarationStatement, SyntaxKind.ForStatement },
            report.Kinds);
        Assert.Equal("Summarize", report.Method?.Identifier.ValueText);
    }

    // ---------------------------------------------------------------------
    // (c) The semantic model's data-flow analysis works on the fixture's
    //     for-loop node — the foundation every classification in yak 02
    //     builds on. (AnalyzeDataFlow on the loop itself walks the bound loop
    //     body; Succeeded == false would mean the scratch compilation or the
    //     selected node cannot be bound.)
    // ---------------------------------------------------------------------
    [Fact]
    public void Fixture_for_loop_supports_data_flow_analysis()
    {
        var (tree, compilation) = LoadFixture();

        var forStatement = tree.GetRoot()
            .DescendantNodes()
            .OfType<ForStatementSyntax>()
            .Single(n => EnclosingMethodName(n) == "Summarize");

        var dataFlow = compilation.GetSemanticModel(tree).AnalyzeDataFlow(forStatement);

        Assert.True(dataFlow.Succeeded);
    }

    // ---------------------------------------------------------------------
    // Acceptance also demands "clean error otherwise": selecting only the
    // for-loop header line (line 69) splits the statement and must fail with
    // a readable reason instead of a crash or a silent wrong count.
    // ---------------------------------------------------------------------
    [Fact]
    public void Range_ending_mid_statement_fails_cleanly()
    {
        var (tree, _) = LoadFixture();

        var report = SelectionResolver.Resolve(tree, 69, 69);

        Assert.False(report.Succeeded);
        Assert.NotNull(report.Error);
        Assert.Contains("no whole", report.Error);
    }

    private static string? EnclosingMethodName(SyntaxNode node) =>
        node.AncestorsAndSelf().OfType<MethodDeclarationSyntax>().FirstOrDefault()?.Identifier.ValueText;
}