dotnet test -e/--environment is not visible to Microsoft.Testing.Platform test process

[cmeeren]

Describe the bug

When using dotnet test in Microsoft.Testing.Platform mode, -e / --environment appears to be accepted by the CLI, but the environment variable is not visible inside the test process.

This affects tests that build .NET host configuration from environment variables. For example, passing -e DOTNET_ENVIRONMENT=Development does not make Host.CreateApplicationBuilder() load appsettings.Development.json; the test process still sees DOTNET_ENVIRONMENT as unset.

Setting the same environment variable in the shell before invoking dotnet test works.

Related MTP tracking issue: #45927

To Reproduce

Minimal project:

global.json:

{
  "test": {
    "runner": "Microsoft.Testing.Platform"
  }
}

MtpEnvRepro.Tests.csproj:

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <TargetFramework>net10.0</TargetFramework>
    <UseMicrosoftTestingPlatformRunner>true</UseMicrosoftTestingPlatformRunner>
    <ImplicitUsings>enable</ImplicitUsings>
    <Nullable>enable</Nullable>
    <IsPackable>false</IsPackable>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="xunit.v3.core.mtp-v2" Version="3.2.2" />
  </ItemGroup>
</Project>

EnvironmentTests.cs:

using Xunit;

public sealed class EnvironmentTests
{
    private static readonly string AtTypeInit =
        Environment.GetEnvironmentVariable("DOTNET_ENVIRONMENT") ?? "<null>";

    [Fact]
    public void Dotnet_environment_is_visible()
    {
        var duringTest =
            Environment.GetEnvironmentVariable("DOTNET_ENVIRONMENT") ?? "<null>";

        Assert.Equal("Development", AtTypeInit);
        Assert.Equal("Development", duringTest);
    }
}

Run:

dotnet test --project MtpEnvRepro.Tests.csproj -e DOTNET_ENVIRONMENT=Development

Actual result: the test fails because DOTNET_ENVIRONMENT is <null>.

Also reproduced with:

dotnet test --project MtpEnvRepro.Tests.csproj --environment DOTNET_ENVIRONMENT=Development

This works as expected:

$env:DOTNET_ENVIRONMENT = 'Development'
dotnet test --project MtpEnvRepro.Tests.csproj

Expected result: variables passed through dotnet test -e/--environment should be visible to the MTP test process, or the option should not be accepted/advertised for this mode.

Exceptions (if any)

No exception. The test process runs, but the environment variable is missing.

Further technical details

Reproduced with:

• .NET SDK: 10.0.204
• MSBuild: 18.3.3
• Host runtime: 10.0.8
• OS: Windows 10.0.26200, win-x64
• Test runner mode: global.json with "test": { "runner": "Microsoft.Testing.Platform" }
• xUnit package: xunit.v3.core.mtp-v2 3.2.2

[Evangelink]

I reproduced this against SDK 10.0.204 and traced it. tl;dr — this is an SDK-only bug that's already fixed on main by #53306 but not yet backported to any 10.0.x release branch.

Root cause

In src/Cli/dotnet/Commands/Test/MTP/TestApplication.cs::CreateProcessStartInfo, the loop that applies command-line env vars is nested inside if (Module.LaunchSettings is ProjectLaunchProfile):

if (Module.LaunchSettings is ProjectLaunchProfile)
{
    foreach (var entry in Module.LaunchSettings.EnvironmentVariables) { ... }

    // Env variables specified on command line override those specified in launch profile:
    foreach (var (name, value) in TestOptions.EnvironmentVariables)
    {
        processStartInfo.Environment[name] = value;   // <-- never runs without launchSettings.json
    }
    ...
}

Without a launchSettings.json (the common case for test projects), the loop is skipped and -e / --environment is silently dropped.

You can see in the repro that DOTNET_CLI_TEST_COMMAND_WORKING_DIRECTORY (set unconditionally a few lines later) does arrive in the test process, while DOTNET_ENVIRONMENT and any other -e vars do not — confirming this code path is the culprit.

Is it also a testfx/MTP problem?

No. Microsoft.Testing.Platform does not expose any -e / --environment option of its own. The SDK is the sole owner of translating dotnet test -e NAME=VAL into processStartInfo.Environment[NAME] = VAL on the spawned test host. Once the test host starts with the correct environment, MTP / xUnit v3 / etc. behave correctly.

Status

• ✅ Fixed on main by Fix --environment variables not applied to test process without launch profile #53306 (merged 2026-05-19): moves the loop out of the launch-profile block, matching dotnet run behavior. Command-line vars still override launch-profile vars when both are present.
• ❌ Not yet in release/10.0.2xx (where 10.0.204 lives), release/10.0.3xx, or release/10.0.4xx. I'll open backports.

[Evangelink]

Confirmed — fix is in main (#53306) and all targeted 10.0.x release branches:

• release/10.0.1xx: [release/10.0.1xx] Fix --environment variables not applied to test process without launch profile #54613 (merged 2026-06-05)
• release/10.0.2xx: [release/10.0.2xx] Fix --environment variables not applied to test process without launch profile #54430 (merged 2026-05-27)
• release/10.0.3xx: [release/10.0.3xx] Fix --environment variables not applied to test process without launch profile #54429 (merged 2026-05-26)
• release/10.0.4xx: [release/10.0.4xx] Fix --environment variables not applied to test process without launch profile #54428 (merged 2026-05-26)

Closing.