Musify/backend/Tests/Musify.Application.Tests/Users/FollowUserCommandHandlerTests.cs

using ErrorOr;
using Microsoft.EntityFrameworkCore;
using Musify.Application.Tests.TestSupport;
using Musify.Application.Users;
using Xunit;

namespace Musify.Application.Tests.Users
{
    public sealed class FollowUserCommandHandlerTests : HandlerTestBase
    {
        private FollowUserCommandHandler CreateHandler() => new(Database, NoOpLogger<FollowUserCommandHandler>());

        [Fact]
        public async Task Handle_ValidTarget_CreatesFollow()
        {
            var follower = TestEntities.User(1, "follower");
            var followed = TestEntities.User(2, "followed");
            await SeedAsync(follower, followed);

            var result = await CreateHandler().Handle(new FollowUserCommand(follower.Id, followed.Id), TestContext.Current.CancellationToken);

            Assert.False(result.IsError);
            Assert.Single(await Database.UserFollows.ToListAsync(TestContext.Current.CancellationToken));
        }

        [Fact]
        public async Task Handle_AlreadyFollowing_IsIdempotent()
        {
            var follower = TestEntities.User(1, "follower");
            var followed = TestEntities.User(2, "followed");
            await SeedAsync(follower, followed, new Musify.Domain.Entities.UserFollow { FollowerId = follower.Id, FollowedId = followed.Id });

            var result = await CreateHandler().Handle(new FollowUserCommand(follower.Id, followed.Id), TestContext.Current.CancellationToken);

            Assert.False(result.IsError);
            Assert.Single(await Database.UserFollows.ToListAsync(TestContext.Current.CancellationToken));
        }

        [Fact]
        public async Task Handle_SelfFollow_ReturnsValidationError()
        {
            var user = TestEntities.User();
            await SeedAsync(user);

            var result = await CreateHandler().Handle(new FollowUserCommand(user.Id, user.Id), TestContext.Current.CancellationToken);

            Assert.Equal(ErrorType.Validation, result.FirstError.Type);
        }

        [Fact]
        public async Task Handle_TargetMissing_ReturnsNotFound()
        {
            var follower = TestEntities.User();
            await SeedAsync(follower);

            var result = await CreateHandler().Handle(new FollowUserCommand(follower.Id, 404), TestContext.Current.CancellationToken);

            Assert.Equal(ErrorType.NotFound, result.FirstError.Type);
        }
    }
}