如何为ExecuteReaderAsync编写shim？

Question

我有以下方法，并希望为其中所需的功能(包括ExecuteReaderAsync)编写shim：

public async Task<IEnumerable<ApplicationSetting>> LoadSettingsAsync(string[] keys)
{
    await using var sourceConnection = new SqlConnection(_options.Value.StoreConnectionString);
    await sourceConnection.OpenAsync();

    SqlCommand command =
        new SqlCommand(
            SqlStatements.SelectMultipleKeys(_options.Value.DefaultStoreTableName,
                _options.Value.DefaultStoreSchema), sourceConnection);
    command.AddArrayParameters(ColumnNames.Keys, keys);
    var reader = await command.ExecuteReaderAsync();

    List<ApplicationSetting> settings = new();
    while (await reader.ReadAsync())
        settings.Add(new ApplicationSetting(reader[ColumnNames.Key].ToString()!,
            reader[ColumnNames.Value].ToString(), reader[ColumnNames.Type].ToString()!));

    await reader.CloseAsync();
    await sourceConnection.CloseAsync();
    return settings;
}

测试方法：

[Fact]
public async Task LoadSettingsAsync_WhenCall_LoadApplicationSettings()
{
    using (ShimsContext.Create())
    {
        // Arrange
        var keys = new string[] { "key1", "key2" };

        // simulate a connection
        ShimSqlConnection.AllInstances.OpenAsyncCancellationToken = (connection, token) =>
        {
            return Task.FromResult(true);
        };
        //string commandText;

        // shim-Mock all called methods
        ShimSqlCommand.AllInstances.ExecuteReaderAsync = command =>
        {
            return Task.FromResult(???????????????????????);
        };
        var rowCounter = 0;
        ShimSqlDataReader.AllInstances.Read = (sender) =>
        {
            rowCounter++;
            return rowCounter <= 2;
        };

        ShimSqlConnection.AllInstances.Close = connection => { };

        // Act
        var ex = await Record.ExceptionAsync(() =>
            _myClass.LoadSettingsAsync(keys));

        // Assert
        ex.Should().BeNull();
    }
} 

我尝试Substitute.For<SqlDataReader>()来创建实例SqlDataReader，但是它抛出了System.InvalidOperationException

然后我尝试了这个代码：

ShimSqlCommand.AllInstances.ExecuteReaderAsync = async command =>
{
     return new ShimSqlDataReader();
};

但是它会在NullReferenceException行上抛出await reader.ReadAsync() (注意:阅读器有价值)：

Answer 1

以下是我所做的：

ShimSqlCommand.AllInstances.ExecuteReaderAsync = command => Task.FromResult((SqlDataReader)new ShimSqlDataReader());

ExecuteReaderAsync需要一个Task<SqlDataReader>作为返回类型。Task.FromResult()用于Task部分。ShimSqlDataReader是来自ShimBase<SqlDataReader>的派生类，您可以将它转换为SqlDataReader，而不存在任何问题。这个类包含在你不需要自己创建的赝品中。

注意：ShimSqlDataReader可以像这样直接使用：

ShimSqlCommand.AllInstances.ExecuteReader = command => new ShimSqlDataReader();

对于一个ExecuteReader垫片(没有async)。