ersatztv/ErsatzTV.Tests/Integration/SearchIndexMutationCoverageTests.cs

using System.Reflection;
using ErsatzTV.Core.Interfaces.Search;
using ErsatzTV.Infrastructure.Search;
using NUnit.Framework;
using NUnit.Framework.Interfaces;
using Shouldly;

namespace ErsatzTV.Tests.Integration;

/// <summary>
///     ersatztv#824. The defect that produced #824 was not that <c>ElasticSearchIndex</c> was hard to
///     test — it was that NOTHING NOTICED it had no cover. #701 fixed two independent copies of the same
///     <c>UpdateSong</c> logic and pinned one; the suite stayed green, and the gap survived on a
///     hand-written list of what had been covered (namely, one entry).
///     <para>
///         So the covered set is compared against a population DERIVED FROM THE ASSEMBLY rather than
///         restated: a third <see cref="ISearchIndex" /> implementation reddens this test until it is
///         given a mutation fixture of its own. That is
///         <c>testing.guard-derives-population-from-source</c> applied to a test population instead of a
///         file population.
///     </para>
///     <para>
///         <b>Scope, stated rather than implied.</b> The derivation is over the assembly that declares
///         both indexers (<c>ErsatzTV.Infrastructure</c>). An implementation added in a DIFFERENT
///         assembly is outside what this sees — it is not covered and this test cannot say so. Both
///         implementations have lived here since the interface existed, so the narrower scope buys a
///         guard that cannot be defeated by an unrelated assembly load order; widening it to every
///         loaded assembly would be the false-confidence version of the same check.
///     </para>
/// </summary>
[TestFixture]
public class SearchIndexMutationCoverageTests
{
    /// <summary>
    ///     The indexers whose <c>UpdateSong</c> is pinned against the ersatztv#701 mutation. Referenced by
    ///     TYPE, so renaming an indexer or deleting a fixture is a compile error rather than a silent
    ///     divergence.
    /// </summary>
    private static readonly Dictionary<Type, Type> CoveredBy = new()
    {
        [typeof(LuceneSearchIndex)] = typeof(SongIndexerMetadataMutationTests),
        [typeof(ElasticSearchIndex)] = typeof(ElasticSongIndexerMetadataMutationTests)
    };

    [Test]
    public void Every_ISearchIndex_Implementation_Has_A_Metadata_Mutation_Fixture()
    {
        List<Type> implementations = typeof(LuceneSearchIndex).Assembly
            .GetTypes()
            .Where(t => t is { IsAbstract: false, IsInterface: false })
            .Where(t => typeof(ISearchIndex).IsAssignableFrom(t))
            .OrderBy(t => t.FullName, StringComparer.Ordinal)
            .ToList();

        // The set comparison below would ALREADY fail on an empty derivation, because the expected side
        // is non-empty -- so this floor is not load-bearing for correctness and saying it is would be a
        // false claim about a check. It is a DIAGNOSTIC: it separates "the reflection stopped finding
        // types" (a moved type, a renamed interface) from "someone added an indexer", which the set
        // comparison alone reports identically.
        implementations.Count.ShouldBeGreaterThanOrEqualTo(
            2,
            "the ISearchIndex population derivation found almost nothing -- this is the derivation "
            + "breaking, not an indexer being added");

        implementations.ShouldBe(
            CoveredBy.Keys.OrderBy(t => t.FullName, StringComparer.Ordinal),
            ignoreOrder: false,
            "every ISearchIndex implementation needs an UpdateSong metadata-mutation fixture — see "
            + "ersatztv#824, where a second copy of the same logic went uncovered and an Elastic-only "
            + "reintroduction of `metadata.Artists ??= []` left the whole suite green");

        // Comparing the KEYS alone would leave the mapping half-checked: a third indexer could be pointed
        // at an EXISTING fixture, or at a fixture class holding no runnable test, and the set comparison
        // above would still pass. Both are closed here. What NO static check can establish is that the
        // named fixture actually DRIVES its indexer -- that is stated as a residual on this guard rather
        // than implied away, and it is why the record claims a third implementation cannot be added
        // WITHOUT NOTICE, not that it cannot be mis-covered.
        CoveredBy.Values.Distinct().Count().ShouldBe(
            CoveredBy.Count,
            "two indexers are mapped to the SAME fixture, so one of them is not actually covered");

        foreach ((Type indexer, Type fixture) in CoveredBy)
        {
            // Test-ness is decided by NUnit's INTERFACES, not by a hand-listed set of attribute types.
            // A list has to be kept in step with NUnit and silently falsely-reddens whatever it omits --
            // an earlier revision listed TestAttribute alone (so a [TestCase]-only fixture failed), then
            // three types (so a [Theory] one did). ITestBuilder/ISimpleTestBuilder is what NUnit itself
            // dispatches on, so it cannot fall behind the vocabulary.
            //
            // DeclaredOnly is load-bearing: without it a fixture that merely SUBCLASSES another inherits
            // its [Test] and satisfies this while driving the wrong indexer -- and Values.Distinct()
            // cannot catch that, since the two Types differ. Static is included because NUnit runs a
            // public static test method in a non-static fixture, and omitting the flag would falsely
            // redden one.
            const BindingFlags TestMethods =
                BindingFlags.Public | BindingFlags.Instance | BindingFlags.Static | BindingFlags.DeclaredOnly;

            static bool NeverRuns(object[] attributes) =>
                attributes.Any(a => a is ExplicitAttribute or IgnoreAttribute);

            bool declaresARunnableTest = fixture
                .GetMethods(TestMethods)
                .Select(m => m.GetCustomAttributes(inherit: true))
                .Any(attrs =>
                    attrs.Any(a => a is ITestBuilder or ISimpleTestBuilder) && !NeverRuns(attrs));

            declaresARunnableTest.ShouldBeTrue(
                $"{fixture.Name} is named as the mutation fixture for {indexer.Name} but DECLARES no "
                + "runnable test method of its own, so it proves nothing");

            // The same "wired is not running" failure at fixture level, in its three forms: an abstract
            // class NUnit will not instantiate, and [Explicit]/[Ignore]. The indexer population at the top
            // of this method already filters IsAbstract; the fixture side needs the mirror of that.
            // `IsAbstract` ALONE is wrong here and would have been a false red: a C# `static class`
            // compiles to `abstract sealed`, and NUnit runs tests declared in one -- this repo already has
            // such a fixture (`AlternateScheduleSelectorTests`). What must be rejected is an abstract BASE
            // (abstract and NOT sealed), which NUnit cannot instantiate.
            (fixture.IsAbstract && !fixture.IsSealed).ShouldBeFalse(
                $"{fixture.Name} is named as the mutation fixture for {indexer.Name} but is an abstract "
                + "base class, so NUnit never runs it");
            NeverRuns(fixture.GetCustomAttributes(inherit: true)).ShouldBeFalse(
                $"{fixture.Name} is named as the mutation fixture for {indexer.Name} but is [Explicit] or "
                + "[Ignore]d, so it never runs and proves nothing");
        }
    }
}