Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

When using the UseCommonOutputDirectory project property or the OutputPath MSBuild flag, WebApplicationFactory randomly fails to initialize, throwing an InvalidOperationException.

This happens because the MvcTestingAppManifest.json does not have a namespace, so the parallel project builds will override each others file, thereby creating a race condition that only succeeds when the correct manifest is written last.

Expected Behavior

The tests should not randomly fail when using a common output path. There are numerous ways to achieve this, but here are a few suggestions (obviously not all of these may be viable):

• The MvcTestingAppManifest.json should be namespaced to avoid the issue entirely.
• The WebApplicationFactoryContentRoot attribute should be used if the manifest doesn't contain a valid path, not only when the manifest doesn't exist.
• The WebApplicationFactory.SetContentRoot method could be protected virtual to allow replacing the behavior. Alternatively, it should not be called before any of the configuration methods run, which would allow applying the TEST_CONTENTROOT_* setting before the exception is thrown.
• The builder is null branch of WebApplicationFactory.EnsureServer should have some overridable method to configure the deferred host before the content root is set.

Steps To Reproduce

• Checkout the official WebApplicationFactory example.
• Add a new project with some random test class and reference it from the test project.
• Set UseCommonOutputDirectory to true for all projects.
• Build the original project, then the new project. Observe how the MvcTestingAppManifest.json is now missing the entry for the original project.
• Run the tests without building. Observe how the tests throw an exception when the manifest is wrong.

Exceptions (if any)

System.InvalidOperationException : Solution root could not be located using application root

.NET Version

8.0.100

Anything else?

NET SDK:
Version: 8.0.100
Commit: 57efcf1350
Workload version: 8.0.100-manifests.8d38d0cc

Laufzeitumgebung:
OS Name: Windows
OS Version: 10.0.22631
OS Platform: Windows
RID: win-x64
Base Path: C:\Program Files\dotnet\sdk\8.0.100\

Installierte .NET-Workloads:
Workload version: 8.0.100-manifests.8d38d0cc
[maui-windows]
Installationsquelle: VS 17.8.34330.188
Manifestversion: 8.0.3/8.0.100
Manifestpfad: C:\Program Files\dotnet\sdk-manifests\8.0.100\microsoft.net.sdk.maui\8.0.3\WorkloadManifest.json
Installationstyp: Msi

[maccatalyst]
Installationsquelle: VS 17.8.34330.188
Manifestversion: 17.0.8478/8.0.100
Manifestpfad: C:\Program Files\dotnet\sdk-manifests\8.0.100\microsoft.net.sdk.maccatalyst\17.0.8478\WorkloadManifest.json
Installationstyp: Msi

[ios]
Installationsquelle: VS 17.8.34330.188
Manifestversion: 17.0.8478/8.0.100
Manifestpfad: C:\Program Files\dotnet\sdk-manifests\8.0.100\microsoft.net.sdk.ios\17.0.8478\WorkloadManifest.json
Installationstyp: Msi

[android]
Installationsquelle: VS 17.8.34330.188
Manifestversion: 34.0.43/8.0.100
Manifestpfad: C:\Program Files\dotnet\sdk-manifests\8.0.100\microsoft.net.sdk.android\34.0.43\WorkloadManifest.json
Installationstyp: Msi

Host:
Version: 8.0.0
Architecture: x64
Commit: 5535e31a71

.NET SDKs installed:
8.0.100 [C:\Program Files\dotnet\sdk]

.NET runtimes installed:
Microsoft.AspNetCore.App 6.0.25 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 7.0.7 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 7.0.14 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 8.0.0 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.NETCore.App 5.0.17 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 6.0.25 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 6.0.27 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 7.0.7 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 7.0.14 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 8.0.0 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.WindowsDesktop.App 5.0.17 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 6.0.25 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 6.0.27 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 7.0.7 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 7.0.14 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 8.0.0 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

Other architectures found:
x86 [C:\Program Files (x86)\dotnet]
registered at [HKLM\SOFTWARE\dotnet\Setup\InstalledVersions\x86\InstallLocation]

Environment variables:
Not set

global.json file:
Not found