C# 如何模拟 DbContext 而不传递它

Question

我想对我的函数

GetDogName

进行单元测试，这将创建一个新的

DbContext

。我已经有了我的

Mock

的工作

DbContext

，但我无法将它作为参数传递到任何地方。

我可以用函数中的其他内容替换

DbContext context = new()

。但我无法将

DbContext

作为参数传递。

我也检查过工厂是否可行（或其他什么？），但尚未找到解决方案。

static class AnimalsHelper
{
    public static string GetDogName() // I can not pass parameters here
    {
        // I can change this line
        using (DbContext context = new())
        {
            return context.Dogs.First().Name;
        }
    }
}

class UnitTest
{
    [SetUp]
    public void SetUp()
    {
        ContextMock = new Mock<DbContext>();
        Context     = ContextMock.Object;

        ContextMock.Setup(context => context.Dogs).Returns("Rex");
    }

    [Test]
    public void GetDogName_DogName_ReturnsRex()
    {
        var expected = "Rex";
        var actual   = AnimalsHelper.GetDogName();
        Assert.AreEqual(expected, actual);
    }
}

Answer 1

public class AnimalDbContext : DbContext
{
    // !!! Must be virtual
    public virtual DbSet<Dog> Dogs { get; set; }
}

public class AnimalService
{
    private AnimalDbContext _context;

    public AnimalService(AnimalDbContext context) 
    {
        _context = context;
    }

    public string GetDogName()
    {
        return _context.Dogs.FirstOrDefault()?.Name;
    }
}

[TestClass()]
public class AnimalServiceTests
{
    [TestMethod()]
    public void GetDogName_DogName_ReturnsRex()
    {
        var data = new List<Dog>
        {
            new Dog { Name = "Rex" }
        }.AsQueryable();

        var mockSet = new Mock<DbSet<Dog>>();
        mockSet.As<IQueryable<Dog>>().Setup(m => m.Provider).Returns(data.Provider);
        mockSet.As<IQueryable<Dog>>().Setup(m => m.Expression).Returns(data.Expression);
        mockSet.As<IQueryable<Dog>>().Setup(m => m.ElementType).Returns(data.ElementType);
        mockSet.As<IQueryable<Dog>>().Setup(m => m.GetEnumerator()).Returns(() => data.GetEnumerator());

        var mockContext = new Mock<AnimalDbContext>();
        mockContext.Setup(c => c.Dogs).Returns(mockSet.Object);

        var service = new AnimalService(mockContext.Object);
        
        // Arrange
        var dogName = service.GetDogName();

        var actual = "Rex";

        Assert.AreEqual(actual, dogName);
    }
}

Answer 2

我们已经通过

DbContextCreator

类解决了这个问题。

在

IDbContextCreator

中创建

Main

类的实例，然后保持静态。

DbContext

不能作为参数传递到的函数使用此 static 创建者实例来创建新的

DbContext

。

在单元测试中，使用了一个创建者类，它返回一个

DbContextMock
。这允许在不访问数据库的情况下测试功能。

主要

internal static class Program
{
    /// <summary>
    ///     Main application entry point
    /// </summary>
    internal static async Task Main(string[] args)
    {
        DbContextCreator.Instance = new MyDbContextCreator();

        // Start Application
    }

    /// <inheritdoc />
    private class MyDbContextCreator : IDbContextCreator
    {
        /// <inheritdoc />
        public BaseDbContext Create() => new();
    }
}

功能

public static void TestableFunction()
{
    using (BaseDbContext context = DbContextCreator.Create())
    {
        // DB stuff
        context.SaveChanges();
    }
}

抽象单元测试

public abstract class AbstractTestWithMockData : AbstractTest
{
    protected BaseDbContext       Context     { get; set; }
    protected Mock<BaseDbContext> ContextMock { get; set; }

    /// <inheritdoc />
    protected AbstractTestWithMockData()
    {
        DbContextCreator.Instance = new TestDbContextCreator(this);
    }

    /// <inheritdoc />
    [SetUp]
    public override void SetUp()
    {
        base.SetUp();

        ContextMock = new Mock<BaseDbContext>();
        Context     = ContextMock.Object;

        // ContextMock.Setup()
    }

    /// <inheritdoc />
    private class TestDbContextCreator : IDbContextCreator
    {
        private readonly AbstractTestWithMockData AbstractTest;

        public TestDbContextCreator(AbstractTestWithMockData abstractTest)
        {
            AbstractTest = abstractTest;
        }

        /// <inheritdoc />
        public BaseDbContext Create()
        {
            return AbstractTest.Context;
        }
    }
}

创作者

Interface

和

static

Instance

/// <summary>
///     Interface for a project-specific implementation of a <see cref="BaseDbContext" /> creator.<br />
///     The creator is required in order to be able to unit test functions
///     where a <see cref="BaseDbContext" /> cannot be passed as a parameter.
/// </summary>
public interface IDbContextCreator
{
    BaseDbContext Create();
}

/// <summary>
///     Static database creator that holds an instance of <see cref="IDbContextCreator" />
///     to be able to create an instance of <see cref="BaseDbContext" />.
/// </summary>
public static class DbContextCreator
{
    /// <summary>
    ///     Static instance of <see cref="IDbContextCreator" /> for the <see cref="Create" /> function.
    /// </summary>
    [SuppressMessage("Design", "CA1044:Properties should not be write only")]
    public static IDbContextCreator? Instance { private get; set; }

    /// <summary>
    ///     Creates a new instance of <see cref="BaseDbContext" />.
    /// </summary>
    /// <returns>A new instance of <see cref="BaseDbContext" /></returns>
    /// <exception cref="Exception">When the <see cref="Instance" /> is not set</exception>
    public static BaseDbContext Create()
    {
        if (Instance is null)
        {
            throw new Exception("Database creator instance is not set! Covfefe!");
        }

        return Instance.Create();
    }
}