让EF Core将SQL语句输出到xUnit的ITestOutputHelper。

Question

我正在使用EF Core 2.2.4，并试图找出EF Core在我们的单元测试中向我们的SQLite数据库发送哪些SQL语句。由于我们使用的是xUnit (2.4.1)，我们必须将日志信息写到 ITestOutputHelper 实例xUnit被注入到我们的测试类中，而不是控制台。对于控制台，我发现了这样的代码。

private static ILoggerFactory GetLoggerFactory()
{
    IServiceCollection serviceCollection = new ServiceCollection();
    serviceCollection.AddLogging(builder =>
        builder.AddConsole()
            .AddFilter(DbLoggerCategory.Database.Command.Name,
                LogLevel.Information));
    return serviceCollection.BuildServiceProvider()
        .GetService<ILoggerFactory>();
}

我要怎么做才能把这个输出重定向到... ITestOutputHelper.WriteLine()?

Answer 1

首先，创建一些模板日志代码，以允许输出到ITestOutputHelper。

class TestLoggerProvider : ILoggerProvider
{
    ITestOutputHelper _output;

    public TestLoggerProvider(ITestOutputHelper output)
        => _output = output;

    public ILogger CreateLogger(string categoryName)
        => new TestLogger(categoryName, _output);

    public void Dispose()
    {
    }
}

class TestLogger : ILogger
{
    string _categoryName;
    ITestOutputHelper _output;

    public TestLogger(string categoryName, ITestOutputHelper output)
    {
        _categoryName = categoryName;
        _output = output;
    }

    public bool IsEnabled(LogLevel logLevel)
        // NB: Only logging things related to commands, but you can easily expand
        //     this
        => _categoryName == DbLoggerCategory.Database.Command.Name;

    public void Log<TState>(
        LogLevel logLevel,
        EventId eventId,
        TState state,
        Exception exception,
        Func<TState, Exception, string> formatter)
    {
        // TODO: Customize the formatting even more if you want
        //if (eventId == RelationalEventId.CommandExecuting)
        //{
        //    var structure = (IReadOnlyList<KeyValuePair<string, object>>)state;
        //    var parameters = (string)structure.First(i => i.Key == "parameters")
        //        .Value;
        //    var commandText = (string)structure.First(i => i.Key == "commandText")
        //        .Value;
        //}

        _output.WriteLine(formatter(state, exception));
    }

    public IDisposable BeginScope<TState>(TState state)
        => null;
}

接下来，确保你的DbContext可以接受外部选项。

class MyDbContext : DbContext
{
    public MyDbContext(DbContextOptions<MyDbContext> options)
        : base(options)
    {
    }
}

最后，将其全部连接起来。这里是一个为每个测试创建一个新上下文的例子。使用一个 阶层 或 采集器 以延长上下文的寿命。

public class UnitTest1 : IDisposable
{
    IServiceProvider _serviceProvider;
    MyDbContext _db;

    public UnitTest1(ITestOutputHelper output)
    {
        _serviceProvider = new ServiceCollection()
            .AddLogging(x => x.AddProvider(new TestLoggerProvider(output)))
            .AddEntityFrameworkSqlite()
            .BuildServiceProvider();

        _db = new MyDbContext(
            new DbContextOptionsBuilder<MyDbContext>()
                // Don't call UseLoggerFactory! (a new service provider would be
                // created every time without ever getting disposed)
                .UseInternalServiceProvider(_serviceProvider)
                .UseSqlite("Data Source=:memory:")
                .Options);
    }

    [Fact]
    public void Test1()
    {
        _db.Database.ExecuteSqlRaw("-- Can you see me?");
    }

    public void Dispose()
    {
        _db.Dispose();
        (_serviceProvider as IDisposable)?.Dispose();
    }
}