[fix] Warn when testhost is not found in project deps.json (missing Microsoft.NET.Test.Sdk) by nohwnd · Pull Request #16077 · microsoft/vstest

nohwnd · 2026-05-30T13:14:31Z

🤖 This is an automated fix created by the Issue Triage agent.

Root Cause

When a .NET test project has a proper deps.json and runtimeconfig.dev.json (indicating a managed .NET project), but doesn't reference microsoft.testplatform.testhost in its deps.json, DotnetTestHostManager silently falls back to using the testhost from the vstest.console installation directory. This fallback can succeed at process launch but then fail at runtime with a confusing error like:

An assembly specified in the application dependencies manifest (testhost.deps.json) was not found:
  package: 'testhost', version: '18.0.1-release-...'
  path: 'testhost.dll'

The root cause is typically a missing reference to Microsoft.NET.Test.Sdk in the test project, but the error message gives no indication of this.

Fix

Added a user-visible Warning message emitted by DotnetTestHostManager.GetTestHostStartInfo when:

The test project has a deps.json file (managed project), AND
The test project has a runtimeconfig.dev.json file (proper SDK-style .NET project), AND
testhost.dll is not found in the project's deps.json (i.e., Microsoft.NET.Test.Sdk is likely missing)

The warning reads:

Test source '{0}' does not include the test host assembly 'testhost.dll'. This can happen when the test project does not reference the 'Microsoft.NET.Test.Sdk' NuGet package. Falling back to the test host from the test runner installation, which may fail if the versions are incompatible.

This warning is shown before the fallback occurs, giving the user actionable information to diagnose the real cause of any subsequent failure.

Changes

DotnetTestHostManager: Added _messageLogger field to store the logger passed to Initialize(), and emit a warning when falling back to runner-side testhost with evidence of a managed project that lacks Microsoft.NET.Test.Sdk.
Resources.resx + Resources.Designer.cs: Added MissingTestSdkWarning resource string.
All .xlf files updated with the new resource string.

🔍 Triaged by Issue Repro Triage & Auto-Fix 🔍

…NET.Test.Sdk) When a .NET test project has a deps.json and runtimeconfig.dev.json (indicating a proper managed project) but the testhost package is not listed in its deps.json, vstest silently falls back to the testhost from the test runner installation. This fallback can cause confusing runtime errors about assembly version mismatches in testhost.deps.json when the versions are incompatible. This change emits a user-visible warning in that scenario, helping users diagnose the root cause: a missing reference to the 'Microsoft.NET.Test.Sdk' NuGet package. Fixes #15403 Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Copilot

Pull request overview

This PR improves diagnostics in the .NET test host resolution path by warning when a managed test project appears to be missing the Microsoft.NET.Test.Sdk dependency before falling back to the runner-side testhost.dll.

Changes:

Stores the initialized IMessageLogger in DotnetTestHostManager.
Emits a warning when .deps.json and .runtimeconfig.dev.json exist but no project-local testhost is resolved.
Adds the new warning resource to .resx, generated designer code, and all locale .xlf files.

Reviewed changes

Copilot reviewed 15 out of 16 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
`src/Microsoft.TestPlatform.TestHostProvider/Hosting/DotnetTestHostManager.cs`	Adds logger storage and warning emission before fallback testhost resolution.
`src/Microsoft.TestPlatform.TestHostProvider/Resources/Resources.resx`	Adds the new `MissingTestSdkWarning` resource string.
`src/Microsoft.TestPlatform.TestHostProvider/Resources/Resources.Designer.cs`	Adds the strongly typed accessor for the new resource.
`src/Microsoft.TestPlatform.TestHostProvider/Resources/xlf/Resources.cs.xlf`	Adds the new localization unit.
`src/Microsoft.TestPlatform.TestHostProvider/Resources/xlf/Resources.de.xlf`	Adds the new localization unit.
`src/Microsoft.TestPlatform.TestHostProvider/Resources/xlf/Resources.es.xlf`	Adds the new localization unit.
`src/Microsoft.TestPlatform.TestHostProvider/Resources/xlf/Resources.fr.xlf`	Adds the new localization unit.
`src/Microsoft.TestPlatform.TestHostProvider/Resources/xlf/Resources.it.xlf`	Adds the new localization unit.
`src/Microsoft.TestPlatform.TestHostProvider/Resources/xlf/Resources.ja.xlf`	Adds the new localization unit.
`src/Microsoft.TestPlatform.TestHostProvider/Resources/xlf/Resources.ko.xlf`	Adds the new localization unit.
`src/Microsoft.TestPlatform.TestHostProvider/Resources/xlf/Resources.pl.xlf`	Adds the new localization unit.
`src/Microsoft.TestPlatform.TestHostProvider/Resources/xlf/Resources.pt-BR.xlf`	Adds the new localization unit.
`src/Microsoft.TestPlatform.TestHostProvider/Resources/xlf/Resources.ru.xlf`	Adds the new localization unit.
`src/Microsoft.TestPlatform.TestHostProvider/Resources/xlf/Resources.tr.xlf`	Adds the new localization unit.
`src/Microsoft.TestPlatform.TestHostProvider/Resources/xlf/Resources.zh-Hans.xlf`	Adds the new localization unit.
`src/Microsoft.TestPlatform.TestHostProvider/Resources/xlf/Resources.zh-Hant.xlf`	Adds the new localization unit.

Files not reviewed (1)

src/Microsoft.TestPlatform.TestHostProvider/Resources/Resources.Designer.cs: Language not supported

+                if (_fileHelper.Exists(depsFilePath) && _fileHelper.Exists(runtimeConfigDevPath))
+                {
+                    string message = string.Format(CultureInfo.CurrentCulture, Resources.MissingTestSdkWarning, sourcePath);
+                    EqtTrace.Warning("DotnetTestHostManager.GetTestHostStartInfo: {0}", message);
+                    _messageLogger?.SendMessage(TestMessageLevel.Warning, message);


+                if (_fileHelper.Exists(depsFilePath) && _fileHelper.Exists(runtimeConfigDevPath))
+                {
+                    string message = string.Format(CultureInfo.CurrentCulture, Resources.MissingTestSdkWarning, sourcePath);
+                    EqtTrace.Warning("DotnetTestHostManager.GetTestHostStartInfo: {0}", message);


nohwnd

Review Summary

Dimensions activated: Process Architecture & Host Resolution · Testhost Assembly Loading & Resolution · Error Reporting & Diagnostic Clarity

What was checked

Testhost Assembly Loading & Resolution — The warning condition (depsFilePath exists AND runtimeConfigDevPath exists AND GetTestHostPath returned empty) is a sound heuristic. runtimeconfig.dev.json only appears in development builds of SDK-style projects, so its presence is a reliable signal that Microsoft.NET.Test.Sdk should be referenced. The fallback path logic is unchanged and correct.

Process Architecture & Host Resolution — Flow analysis confirms the warning fires only when both GetTestHostPath calls return empty and we're about to fall back to the runner-side testhost. On Windows, if testHostPath was set from the nuget-based lookup at line 338 (even without a testHostExeFound), the warning is correctly suppressed at line 375 since testHostPath.IsNullOrEmpty() is false.

Error Reporting & Diagnostic Clarity — The user-visible message is accurate and actionable. One minor issue noted inline: the EqtTrace.Warning call uses GetTestHostStartInfo rather than the actual method name GetTestHostProcessStartInfo.

_messageLogger null safety — The ?. guard is appropriate; Initialize() can be called with a null logger and this is handled safely.

No public API changes — _messageLogger is private; Resources.MissingTestSdkWarning is internal. No PublicAPI.Unshipped.txt update needed.

Localization — All 12 .xlf files correctly updated with state="new" per convention.

One minor inline finding (incorrect trace method name). No blocking issues.

🧠 Reviewed by Expert Code Reviewer

🧠 Reviewed by Expert Code Reviewer 🧠

nohwnd · 2026-05-30T13:20:28Z

+                if (_fileHelper.Exists(depsFilePath) && _fileHelper.Exists(runtimeConfigDevPath))
+                {
+                    string message = string.Format(CultureInfo.CurrentCulture, Resources.MissingTestSdkWarning, sourcePath);
+                    EqtTrace.Warning("DotnetTestHostManager.GetTestHostStartInfo: {0}", message);


[Error Reporting & Diagnostic Clarity] The EqtTrace.Warning call uses the method name GetTestHostStartInfo, but the actual method is GetTestHostProcessStartInfo. This won't affect user-visible output, but it makes log correlation harder when debugging.

// Current (incorrect method name) EqtTrace.Warning("DotnetTestHostManager.GetTestHostStartInfo: {0}", message); // Should be: EqtTrace.Warning("DotnetTestHostManager.GetTestHostProcessStartInfo: {0}", message);

Fixed — updated the EqtTrace.Warning call to use GetTestHostProcessStartInfo as the method name.

🔧 Iterated by PR Iteration Agent 🔧

…rtInfo Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

nohwnd · 2026-05-30T13:25:06Z

Commit pushed: b7cf13d

🔧 Iterated by PR Iteration Agent 🔧

Copilot AI review requested due to automatic review settings May 30, 2026 13:14

Copilot started reviewing on behalf of nohwnd May 30, 2026 13:14 View session

Copilot AI reviewed May 30, 2026

View reviewed changes

nohwnd commented May 30, 2026

View reviewed changes

fix: correct method name in EqtTrace.Warning to GetTestHostProcessSta…

b7cf13d

…rtInfo Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

nohwnd mentioned this pull request May 31, 2026

Daily Maintenance Digest — 2026-06-01 #16066

Open

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

[fix] Warn when testhost is not found in project deps.json (missing Microsoft.NET.Test.Sdk)#16077

[fix] Warn when testhost is not found in project deps.json (missing Microsoft.NET.Test.Sdk)#16077
nohwnd wants to merge 2 commits into
mainfrom
fix/issue-15403-1a4d5a5e2fb34035

nohwnd commented May 30, 2026

Uh oh!

Copilot AI left a comment

Uh oh!

nohwnd left a comment

Uh oh!

nohwnd May 30, 2026

Uh oh!

nohwnd May 30, 2026

Uh oh!

nohwnd commented May 30, 2026

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

2 participants

Conversation

nohwnd commented May 30, 2026

Root Cause

Fix

Changes

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

Pull request overview

Reviewed changes

Uh oh!

nohwnd left a comment

Choose a reason for hiding this comment

Review Summary

What was checked

Uh oh!

nohwnd May 30, 2026

Choose a reason for hiding this comment

Uh oh!

nohwnd May 30, 2026

Choose a reason for hiding this comment

Uh oh!

nohwnd commented May 30, 2026

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

2 participants