将Visual Studio 2019更新为16.4.0之后，我无法使用目标框架2.2运行测试

我已经更新Visual studio 2019到版本16.4.0。此版本包括.NET Core SDK3.1.100。

在那之后，我尝试在Target Framework2.2版本的项目上运行一些单元测试，但是无法执行。它给出以下错误：

Microsoft.VisualStudio.TestPlatform.ObjectModel.TestPlatformException: Testhost process exited with error: It was not possible to find any compatible framework version
The framework 'Microsoft.AspNetCore.App', version '2.2.0' was not found.
  - The following frameworks were found:
      3.1.0 at [C:\Program Files (x86)\dotnet\shared\Microsoft.AspNetCore.App]
You can resolve the problem by installing the specified framework and/or SDK.

如果转到上述路径，我只会找到3.1.0文件夹。如果列出已安装的SDKS，则会得到以下信息：

dotnet --list-sdks 
2.1.602 [C:\Program Files\dotnet\sdk]
2.1.700 [C:\Program Files\dotnet\sdk]
2.1.701 [C:\Program Files\dotnet\sdk]
2.1.801 [C:\Program Files\dotnet\sdk]
2.1.802 [C:\Program Files\dotnet\sdk]
2.2.100 [C:\Program Files\dotnet\sdk]
2.2.202 [C:\Program Files\dotnet\sdk]
2.2.207 [C:\Program Files\dotnet\sdk]
2.2.300 [C:\Program Files\dotnet\sdk]
2.2.301 [C:\Program Files\dotnet\sdk]
2.2.401 [C:\Program Files\dotnet\sdk]
2.2.402 [C:\Program Files\dotnet\sdk]
3.1.100 [C:\Program Files\dotnet\sdk]

如果我要求安装的运行时，则会得到以下信息：

dotnet --list-runtimes
Microsoft.AspNetCore.All 2.1.9 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.All 2.1.11 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.All 2.1.12 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.All 2.1.13 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.All 2.2.0 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.All 2.2.3 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.All 2.2.5 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.All 2.2.6 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.All 2.2.7 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.All 2.2.8 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.App 2.1.9 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 2.1.11 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 2.1.12 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 2.1.13 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 2.2.0 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 2.2.3 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 2.2.5 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 2.2.6 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 2.2.7 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 2.2.8 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 3.1.0 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.NETCore.App 2.1.9 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 2.1.11 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 2.1.12 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 2.1.13 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 2.2.0 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 2.2.3 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 2.2.5 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 2.2.6 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 2.2.7 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 2.2.8 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 3.1.0 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.WindowsDesktop.App 3.1.0 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

因此，我在列出的运行时上看到了Microsoft.AspNetCore.App'版本'2.2.0'。

另一方面，如果我这样做：Package Manager Console正在运行测试中的单元测试项目上的“ dotnet测试” 。

我也已经Visual Studio Code安装了并且没有任何更改，我什至可以调试那些测试。

因此，我在这里有点迷失了，例如，我尝试从C：\ Program Files \ dotnet \ shared \手动复制2.2.0文件夹，但是之后，在尝试运行测试时遇到其他错误。

任何人都可以帮助我或为我指明正确的方向。

在查看@coloradoeos的解决方案后，我发现了无需安装x86版本即可解决此问题的另一种方法。

只需转到Test>任何CPU项目的流程体系结构> x64

选择x64后，测试应该可以正常运行。

我将推荐您使用此链接。

根本原因似乎是在以下目录下缺少x86 .NET Core 2.2 SDK实例"C:\Program Files (x86)\dotnet\shared\Microsoft.NETCore.App"。

我只有3.1版本，因此我专门下载了x86版本的2.2 SDK并安装了它。一旦这样做，测试主机就可以从Visual Studio（VS）运行我的单元测试。我从未卸载过旧版本的SDK，因此这一定是框架/ VS更新过程中的问题。