.NET MAUI集成测试：FileNotFoundException无法加载Microsoft.Maui.Essentials

在对使用Entity Framework Core的.NET MAUI应用进行集成测试时，执行到this.Database.EnsureCreated()时抛出文件未找到异常：

System.IO.FileNotFoundException: 'Could not load file or assembly 'Microsoft.Maui.Essentials, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'. The system cannot find the file specified.'

尝试安装Microsoft.Maui.Essentials.Ref系列包时，收到错误：

'The package Microsoft.Maui.Essentials.Ref.any 6.0.547 has a package type DotnetPlatform that is incompatible with this project'

相关代码和项目配置如下：

集成测试代码 #

...
var options = new DbContextOptionsBuilder<DataContext>()
                .UseInMemoryDatabase(databaseName: "Test_Database")
                .Options;
var mockDataContext = new Mock<DataContext>(options);
mockDataContextCreator
    .Setup(x => x.CreateDbContext())
    .Returns(new DataContext(options));
...

DataContext代码 #

public class DataContext : DbContext
...

public DataContext(DbContextOptions options)
    : base(options)
{
    SQLitePCL.Batteries_V2.Init();

    if (!this.Database.EnsureCreated())
    {
        this.Database.Migrate();
    }
}

集成测试项目CSPROJ配置 #

...
<PropertyGroup>
    <TargetFramework>net6.0</TargetFramework>
    <ImplicitUsings>enable</ImplicitUsings>
    <Nullable>enable</Nullable>

    <IsPackable>false</IsPackable>
</PropertyGroup>

<ItemGroup>
    <PackageReference Include="Microsoft.EntityFrameworkCore.InMemory" Version="7.0.0" />
    <PackageReference Include="Microsoft.Maui.Dependencies" Version="6.0.547" />
    <PackageReference Include="Microsoft.Maui.Extensions" Version="6.0.547" />
    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.1.0" />
    <PackageReference Include="Moq" Version="4.18.2" />
    <PackageReference Include="NUnit" Version="3.13.3" />
    <PackageReference Include="NUnit3TestAdapter" Version="4.2.1" />
    <PackageReference Include="NUnit.Analyzers" Version="3.3.0" />
    <PackageReference Include="coverlet.collector" Version="3.1.2" />
</ItemGroup>
...

1. 移除测试项目中不必要的MAUI依赖 #

测试项目为net6.0常规类库，无需引用MAUI专用的Microsoft.Maui.Dependencies和Microsoft.Maui.Extensions包，直接从CSPROJ中删除这两个引用，避免依赖冲突：

<!-- 移除以下两行引用 -->
<PackageReference Include="Microsoft.Maui.Dependencies" Version="6.0.547" />
<PackageReference Include="Microsoft.Maui.Extensions" Version="6.0.547" />

2. 分离SQLite初始化逻辑，避免测试环境触发 #

SQLitePCL.Batteries_V2.Init()是SQLite数据库专用的初始化代码，而测试使用的是内存数据库，完全不需要这一步。将初始化逻辑移到MAUI项目的启动代码中（而非DataContext构造函数）：

修改MAUI项目的Program.cs #

var builder = MauiApp.CreateBuilder();
builder
    .UseMauiApp<App>()
    .ConfigureFonts(fonts =>
    {
        fonts.AddFont("OpenSans-Regular.ttf", "OpenSansRegular");
    });

// 在MAUI启动时初始化SQLite
SQLitePCL.Batteries_V2.Init();

// 注册DataContext等服务
builder.Services.AddDbContext<DataContext>(options =>
    options.UseSqlite("Data Source=MyDatabase.db"));

var app = builder.Build();
app.Run();

修改DataContext构造函数 #

移除SQLite初始化代码，简化构造逻辑：

public DataContext(DbContextOptions options)
    : base(options)
{
    if (!this.Database.EnsureCreated())
    {
        this.Database.Migrate();
    }
}

3. 统一EF Core版本（可选但推荐） #

测试项目使用的Microsoft.EntityFrameworkCore.InMemory版本为7.0.0，而MAUI项目基于net6.0，建议统一使用net6.0对应的EF Core版本（6.x系列），避免跨版本兼容性问题：

<PackageReference Include="Microsoft.EntityFrameworkCore.InMemory" Version="6.0.25" />

4. 简化测试代码（可选） #

测试中无需Mock DataContext，直接实例化即可，内存数据库本身是轻量级的，不会有额外开销：

var options = new DbContextOptionsBuilder<DataContext>()
                .UseInMemoryDatabase(databaseName: "Test_Database")
                .Options;

// 直接实例化DataContext，无需Mock
var dataContext = new DataContext(options);
mockDataContextCreator
    .Setup(x => x.CreateDbContext())
    .Returns(dataContext);

内容的提问来源于stack exchange，提问作者Scott Seto