Microsoft.TestPlatform 18.5.0 net462 Extensions layout ships System.Text.Json without companion dependencies

[quasarea]

Summary

Microsoft.TestPlatform 18.5.0 installs a net462 VsTest Extensions layout that contains System.Text.Json.dll but not the companion assemblies it depends on for .NET Framework resolution. On hosted Azure DevOps runs using VisualStudioTestPlatformInstaller@1 plus VSTest@2 with code coverage, this causes runtime assembly-load failures unless the missing DLLs are staged manually next to the VsTest extensions.

This looks related to, but different from, #15297. That issue is about Microsoft.CodeCoverage copying System.Text.Json.dll into output/publish layouts. This issue is about the installed VsTest tools\\net462\\...\\Extensions runtime layout itself not being a complete dependency closure.

Repro shape

• Azure DevOps hosted agent (windows-latest / Windows Server 2025 repro confirmed)
• VisualStudioTestPlatformInstaller@1
• testPlatformVersion: 18.5.0
• VSTest@2
• code coverage enabled
• native / .NET Framework-oriented test execution path that loads the net462 VsTest extensions

What we observed

The installed TestPlatform package contains:

• tools\\net462\\Common7\\IDE\\Extensions\\TestPlatform\\Extensions\\System.Text.Json.dll

But it does not contain these companion assemblies in the package/runtime layout:

• Microsoft.Bcl.AsyncInterfaces.dll
• System.Text.Encodings.Web.dll
• System.Threading.Tasks.Extensions.dll

We inspected the extracted packages directly:

Microsoft.TestPlatform 18.5.0

• System.Text.Json.dll: present
• Microsoft.Bcl.AsyncInterfaces.dll: absent
• System.Text.Encodings.Web.dll: absent
• System.Threading.Tasks.Extensions.dll: absent

Microsoft.CodeCoverage 17.8.0

• System.Text.Json.dll: absent
• Microsoft.Bcl.AsyncInterfaces.dll: absent
• System.Text.Encodings.Web.dll: absent
• System.Threading.Tasks.Extensions.dll: absent

Separately, the System.Text.Json 6.0.11 nuspec declares these dependencies for .NETFramework4.6.1:

• Microsoft.Bcl.AsyncInterfaces
• System.Text.Encodings.Web
• System.Threading.Tasks.Extensions
• plus other transitive dependencies

So the problem is not that System.Text.Json has no dependency metadata. The problem is that the VsTest net462 extensions runtime layout is not physically self-contained for this load context on hosted agents.

Workaround

Staging these DLLs next to the installed VsTest extensions fixes the hosted-agent failure for us:

• Microsoft.Bcl.AsyncInterfaces.dll (6.0.0, lib\\net461)
• System.Text.Encodings.Web.dll (6.0.0, lib\\net461)
• System.Threading.Tasks.Extensions.dll (4.5.4, lib\\net461)

into:

• VsTest\\18.5.0\\x64\\tools\\net462\\Common7\\IDE\\Extensions\\TestPlatform\\Extensions

We explicitly preserved the VsTest-provided System.Text.Json.dll and only staged the missing companion DLLs.

Why I think this is an upstream packaging/runtime-layout bug

The hosted test run should not require pipeline consumers to reverse-engineer and manually complete the dependency closure for the installed net462 extensions folder. If System.Text.Json.dll is shipped there and loaded from that context, its required companion assemblies should either:

1. be shipped alongside it in the effective runtime layout, or
2. be resolved through a supported, documented binding/probing mechanism that works on hosted Azure DevOps agents

Right now it appears neither is true for this scenario.

Requested outcome

Please confirm whether this is a known gap in the Microsoft.TestPlatform / coverage extension packaging for the net462 extension path, and whether the fix should be:

• adding the missing companion assemblies to the shipped runtime layout, or
• adding/repairing the binding/probing setup so the extension path resolves them correctly without manual staging

[MihuBot]

I'm a bot. Here is a possible related and/or duplicate issue (I may be wrong):

• STJ migration: DesignMode/wrapper communication hangs during test execution #15577

[nohwnd]

@fhnaseer This is not a regression between 18.4.0 and 18.5.0 — the Extensions folder is identical across all v18 releases. The situation:

• v17.14.1: No System.Text.Json.dll in Extensions (no problem).
• v18.0.1 → 18.5.1: System.Text.Json.dll and System.Memory.dll were added to the net462 Extensions folder, but the companion deps (Microsoft.Bcl.AsyncInterfaces, System.Text.Encodings.Web, System.Threading.Tasks.Extensions) were never included.

So STJ has been shipped without its net462 companion dependencies since v18.0.1. The removed DLLs from v17 → v18 were unrelated (CodedWebTestAdapter, TmiAdapter, WebTestAdapter, VideoRecorderCollector, MediaRecorder.Model).

Can you take a look at whether those companion assemblies should be added to the Extensions layout?

[nohwnd]

Triage Analysis 🤖

This is a confirmed packaging issue in Microsoft.TestPlatform 18.5.0.

Root cause: The net462 Extensions layout ships System.Text.Json.dll but omits its required companion assemblies for .NET Framework:

• Microsoft.Bcl.AsyncInterfaces.dll
• System.Text.Encodings.Web.dll
• System.Threading.Tasks.Extensions.dll

System.Text.Json for net461 targets depends on all three of these. Without them in the same probing path as the extensions folder, the runtime assembly loader fails when System.Text.Json is loaded in the net462 context (which has no assembly redirect infrastructure on hosted Azure DevOps agents).

Fix direction: The net462 extensions layout should include these companion assemblies alongside System.Text.Json.dll. This requires updating the packaging/layout build scripts to include these DLLs. The companion assemblies should be sourced from the same package version used for System.Text.Json (6.0.x): Microsoft.Bcl.AsyncInterfaces 6.0.0 (lib/net461), System.Text.Encodings.Web 6.0.0 (lib/net461), and System.Threading.Tasks.Extensions 4.5.4 (lib/net461).

Workaround (as described by the reporter): Manually stage these three DLLs into the VsTest extensions folder.

🔍 Triaged by Issue Repro Triage & Auto-Fix 🔍

[nohwnd]

Pull request created: #15772

🔍 Triaged by Issue Repro Triage & Auto-Fix 🔍

[nohwnd]

Automated Fix 🤖

I've created a PR to fix this issue: the net462 Extensions layout was shipping System.Text.Json.dll without its required .NET Framework companion assemblies.

Root cause confirmed: Microsoft.Bcl.AsyncInterfaces.dll, System.Text.Encodings.Web.dll, and System.Threading.Tasks.Extensions.dll were never added to the Extensions\TestPlatform\ folder alongside System.Text.Json.dll, causing assembly load failures on .NET Framework hosts with no binding redirect infrastructure (e.g. hosted Azure DevOps DTA agents).

Fix: Added the three companion DLLs to both:

• Microsoft.TestPlatform.nuspec (tools\net462\Common7\IDE\Extensions\TestPlatform\)
• Microsoft.VisualStudio.TestTools.TestPlatform.V2.CLI.csproj (VSIX)

🔍 Fixed by Issue Repro Triage & Auto-Fix 🔍

🔍 Triaged by Issue Repro Triage & Auto-Fix 🔍

[nohwnd]

Should be fixed by the next insertion of CC according to faisal. Don't touch anymore.