microsoft · nohwnd · May 22, 2026
diff --git a/src/Microsoft.TestPlatform.TestHostProvider/Hosting/DotnetTestHostManager.cs b/src/Microsoft.TestPlatform.TestHostProvider/Hosting/DotnetTestHostManager.cs
@@ -459,7 +459,8 @@ public virtual TestProcessStartInfo GetTestHostProcessStartInfo(
 
             if (testHostPath.IsNullOrEmpty())
             {
-                throw new TestPlatformException("Could not find testhost");
+                string message = string.Format(CultureInfo.CurrentCulture, Resources.CouldNotFindTesthost, sourcePath, sourceDirectory);
+                throw new TestPlatformException(message);
             }
 
             // We silently force x64 only if the target architecture is the default one and is not specified by user

diff --git a/src/Microsoft.TestPlatform.TestHostProvider/Resources/Resources.Designer.cs b/src/Microsoft.TestPlatform.TestHostProvider/Resources/Resources.Designer.cs
diff --git a/src/Microsoft.TestPlatform.TestHostProvider/Resources/Resources.resx b/src/Microsoft.TestPlatform.TestHostProvider/Resources/Resources.resx
@@ -127,6 +127,16 @@
   <data name="SuggestPublishTestProject" xml:space="preserve">
     <value>Unable to find {0}. Please publish your test project and retry.</value>
   </data>
+  <data name="CouldNotFindTesthost" xml:space="preserve">
+    <value>Could not find testhost for test source '{0}'.
+
+Verify that:
+  - The test project references the 'Microsoft.NET.Test.Sdk' NuGet package.
+  - The project has been built and the output is in '{1}'.
+  - The project's target framework matches the installed .NET runtime.
+</value>
+    <comment>'{0}' is the path to the test source (DLL/EXE), '{1}' is the directory where testhost was searched.</comment>
+  </data>
   <data name="NoDotnetMuxerFoundForArchitecture" xml:space="preserve">
     <value>Could not find '{0}' host for the '{1}' architecture.
 

diff --git a/src/Microsoft.TestPlatform.TestHostProvider/Resources/xlf/Resources.cs.xlf b/src/Microsoft.TestPlatform.TestHostProvider/Resources/xlf/Resources.cs.xlf
@@ -2,6 +2,23 @@
 <xliff xmlns="urn:oasis:names:tc:xliff:document:1.2" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" version="1.2" xsi:schemaLocation="urn:oasis:names:tc:xliff:document:1.2 xliff-core-1.2-transitional.xsd">
   <file datatype="xml" source-language="en" original="../Resources.resx" target-language="cs">
     <body>
+      <trans-unit id="CouldNotFindTesthost">
+        <source>Could not find testhost for test source '{0}'.
+
+Verify that:
+  - The test project references the 'Microsoft.NET.Test.Sdk' NuGet package.
+  - The project has been built and the output is in '{1}'.
+  - The project's target framework matches the installed .NET runtime.
+</source>
+        <target state="new">Could not find testhost for test source '{0}'.
+
+Verify that:
+  - The test project references the 'Microsoft.NET.Test.Sdk' NuGet package.
+  - The project has been built and the output is in '{1}'.
+  - The project's target framework matches the installed .NET runtime.
+</target>
+        <note>'{0}' is the path to the test source (DLL/EXE), '{1}' is the directory where testhost was searched.</note>
+      </trans-unit>
       <trans-unit id="MultipleFileVersions">
         <source>Multiple versions of same extension found. Selecting the highest version.
 {0}</source>

diff --git a/src/Microsoft.TestPlatform.TestHostProvider/Resources/xlf/Resources.de.xlf b/src/Microsoft.TestPlatform.TestHostProvider/Resources/xlf/Resources.de.xlf
@@ -2,6 +2,23 @@
 <xliff xmlns="urn:oasis:names:tc:xliff:document:1.2" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" version="1.2" xsi:schemaLocation="urn:oasis:names:tc:xliff:document:1.2 xliff-core-1.2-transitional.xsd">
   <file datatype="xml" source-language="en" original="../Resources.resx" target-language="de">
     <body>
+      <trans-unit id="CouldNotFindTesthost">
+        <source>Could not find testhost for test source '{0}'.
+
+Verify that:
+  - The test project references the 'Microsoft.NET.Test.Sdk' NuGet package.
+  - The project has been built and the output is in '{1}'.
+  - The project's target framework matches the installed .NET runtime.
+</source>
+        <target state="new">Could not find testhost for test source '{0}'.
+
+Verify that:
+  - The test project references the 'Microsoft.NET.Test.Sdk' NuGet package.
+  - The project has been built and the output is in '{1}'.
+  - The project's target framework matches the installed .NET runtime.
+</target>
+        <note>'{0}' is the path to the test source (DLL/EXE), '{1}' is the directory where testhost was searched.</note>
+      </trans-unit>
       <trans-unit id="MultipleFileVersions">
         <source>Multiple versions of same extension found. Selecting the highest version.
 {0}</source>

diff --git a/src/Microsoft.TestPlatform.TestHostProvider/Resources/xlf/Resources.es.xlf b/src/Microsoft.TestPlatform.TestHostProvider/Resources/xlf/Resources.es.xlf
@@ -2,6 +2,23 @@
 <xliff xmlns="urn:oasis:names:tc:xliff:document:1.2" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" version="1.2" xsi:schemaLocation="urn:oasis:names:tc:xliff:document:1.2 xliff-core-1.2-transitional.xsd">
   <file datatype="xml" source-language="en" original="../Resources.resx" target-language="es">
     <body>
+      <trans-unit id="CouldNotFindTesthost">
+        <source>Could not find testhost for test source '{0}'.
+
+Verify that:
+  - The test project references the 'Microsoft.NET.Test.Sdk' NuGet package.
+  - The project has been built and the output is in '{1}'.
+  - The project's target framework matches the installed .NET runtime.
+</source>
+        <target state="new">Could not find testhost for test source '{0}'.
+
+Verify that:
+  - The test project references the 'Microsoft.NET.Test.Sdk' NuGet package.
+  - The project has been built and the output is in '{1}'.
+  - The project's target framework matches the installed .NET runtime.
+</target>
+        <note>'{0}' is the path to the test source (DLL/EXE), '{1}' is the directory where testhost was searched.</note>
+      </trans-unit>
       <trans-unit id="MultipleFileVersions">
         <source>Multiple versions of same extension found. Selecting the highest version.
 {0}</source>

diff --git a/src/Microsoft.TestPlatform.TestHostProvider/Resources/xlf/Resources.fr.xlf b/src/Microsoft.TestPlatform.TestHostProvider/Resources/xlf/Resources.fr.xlf
@@ -2,6 +2,23 @@
 <xliff xmlns="urn:oasis:names:tc:xliff:document:1.2" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" version="1.2" xsi:schemaLocation="urn:oasis:names:tc:xliff:document:1.2 xliff-core-1.2-transitional.xsd">
   <file datatype="xml" source-language="en" original="../Resources.resx" target-language="fr">
     <body>
+      <trans-unit id="CouldNotFindTesthost">
+        <source>Could not find testhost for test source '{0}'.
+
+Verify that:
+  - The test project references the 'Microsoft.NET.Test.Sdk' NuGet package.
+  - The project has been built and the output is in '{1}'.
+  - The project's target framework matches the installed .NET runtime.
+</source>
+        <target state="new">Could not find testhost for test source '{0}'.
+
+Verify that:
+  - The test project references the 'Microsoft.NET.Test.Sdk' NuGet package.
+  - The project has been built and the output is in '{1}'.
+  - The project's target framework matches the installed .NET runtime.
+</target>
+        <note>'{0}' is the path to the test source (DLL/EXE), '{1}' is the directory where testhost was searched.</note>
+      </trans-unit>
       <trans-unit id="MultipleFileVersions">
         <source>Multiple versions of same extension found. Selecting the highest version.
 {0}</source>

diff --git a/src/Microsoft.TestPlatform.TestHostProvider/Resources/xlf/Resources.it.xlf b/src/Microsoft.TestPlatform.TestHostProvider/Resources/xlf/Resources.it.xlf
@@ -2,6 +2,23 @@
 <xliff xmlns="urn:oasis:names:tc:xliff:document:1.2" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" version="1.2" xsi:schemaLocation="urn:oasis:names:tc:xliff:document:1.2 xliff-core-1.2-transitional.xsd">
   <file datatype="xml" source-language="en" original="../Resources.resx" target-language="it">
     <body>
+      <trans-unit id="CouldNotFindTesthost">
+        <source>Could not find testhost for test source '{0}'.
+
+Verify that:
+  - The test project references the 'Microsoft.NET.Test.Sdk' NuGet package.
+  - The project has been built and the output is in '{1}'.
+  - The project's target framework matches the installed .NET runtime.
+</source>
+        <target state="new">Could not find testhost for test source '{0}'.
+
+Verify that:
+  - The test project references the 'Microsoft.NET.Test.Sdk' NuGet package.
+  - The project has been built and the output is in '{1}'.
+  - The project's target framework matches the installed .NET runtime.
+</target>
+        <note>'{0}' is the path to the test source (DLL/EXE), '{1}' is the directory where testhost was searched.</note>
+      </trans-unit>
       <trans-unit id="MultipleFileVersions">
         <source>Multiple versions of same extension found. Selecting the highest version.
 {0}</source>

diff --git a/src/Microsoft.TestPlatform.TestHostProvider/Resources/xlf/Resources.ja.xlf b/src/Microsoft.TestPlatform.TestHostProvider/Resources/xlf/Resources.ja.xlf
@@ -2,6 +2,23 @@
 <xliff xmlns="urn:oasis:names:tc:xliff:document:1.2" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" version="1.2" xsi:schemaLocation="urn:oasis:names:tc:xliff:document:1.2 xliff-core-1.2-transitional.xsd">
   <file datatype="xml" source-language="en" original="../Resources.resx" target-language="ja">
     <body>
+      <trans-unit id="CouldNotFindTesthost">
+        <source>Could not find testhost for test source '{0}'.
+
+Verify that:
+  - The test project references the 'Microsoft.NET.Test.Sdk' NuGet package.
+  - The project has been built and the output is in '{1}'.
+  - The project's target framework matches the installed .NET runtime.
+</source>
+        <target state="new">Could not find testhost for test source '{0}'.
+
+Verify that:
+  - The test project references the 'Microsoft.NET.Test.Sdk' NuGet package.
+  - The project has been built and the output is in '{1}'.
+  - The project's target framework matches the installed .NET runtime.
+</target>
+        <note>'{0}' is the path to the test source (DLL/EXE), '{1}' is the directory where testhost was searched.</note>
+      </trans-unit>
       <trans-unit id="MultipleFileVersions">
         <source>Multiple versions of same extension found. Selecting the highest version.
 {0}</source>

diff --git a/src/Microsoft.TestPlatform.TestHostProvider/Resources/xlf/Resources.ko.xlf b/src/Microsoft.TestPlatform.TestHostProvider/Resources/xlf/Resources.ko.xlf
@@ -2,6 +2,23 @@
 <xliff xmlns="urn:oasis:names:tc:xliff:document:1.2" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" version="1.2" xsi:schemaLocation="urn:oasis:names:tc:xliff:document:1.2 xliff-core-1.2-transitional.xsd">
   <file datatype="xml" source-language="en" original="../Resources.resx" target-language="ko">
     <body>
+      <trans-unit id="CouldNotFindTesthost">
+        <source>Could not find testhost for test source '{0}'.
+
+Verify that:
+  - The test project references the 'Microsoft.NET.Test.Sdk' NuGet package.
+  - The project has been built and the output is in '{1}'.
+  - The project's target framework matches the installed .NET runtime.
+</source>
+        <target state="new">Could not find testhost for test source '{0}'.
+
+Verify that:
+  - The test project references the 'Microsoft.NET.Test.Sdk' NuGet package.
+  - The project has been built and the output is in '{1}'.
+  - The project's target framework matches the installed .NET runtime.
+</target>
+        <note>'{0}' is the path to the test source (DLL/EXE), '{1}' is the directory where testhost was searched.</note>
+      </trans-unit>
       <trans-unit id="MultipleFileVersions">
         <source>Multiple versions of same extension found. Selecting the highest version.
 {0}</source>

diff --git a/src/Microsoft.TestPlatform.TestHostProvider/Resources/xlf/Resources.pl.xlf b/src/Microsoft.TestPlatform.TestHostProvider/Resources/xlf/Resources.pl.xlf
@@ -2,6 +2,23 @@
 <xliff xmlns="urn:oasis:names:tc:xliff:document:1.2" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" version="1.2" xsi:schemaLocation="urn:oasis:names:tc:xliff:document:1.2 xliff-core-1.2-transitional.xsd">
   <file datatype="xml" source-language="en" original="../Resources.resx" target-language="pl">
     <body>
+      <trans-unit id="CouldNotFindTesthost">
+        <source>Could not find testhost for test source '{0}'.
+
+Verify that:
+  - The test project references the 'Microsoft.NET.Test.Sdk' NuGet package.
+  - The project has been built and the output is in '{1}'.
+  - The project's target framework matches the installed .NET runtime.
+</source>
+        <target state="new">Could not find testhost for test source '{0}'.
+
+Verify that:
+  - The test project references the 'Microsoft.NET.Test.Sdk' NuGet package.
+  - The project has been built and the output is in '{1}'.
+  - The project's target framework matches the installed .NET runtime.
+</target>
+        <note>'{0}' is the path to the test source (DLL/EXE), '{1}' is the directory where testhost was searched.</note>
+      </trans-unit>
       <trans-unit id="MultipleFileVersions">
         <source>Multiple versions of same extension found. Selecting the highest version.
 {0}</source>

diff --git a/src/Microsoft.TestPlatform.TestHostProvider/Resources/xlf/Resources.pt-BR.xlf b/src/Microsoft.TestPlatform.TestHostProvider/Resources/xlf/Resources.pt-BR.xlf
@@ -2,6 +2,23 @@
 <xliff xmlns="urn:oasis:names:tc:xliff:document:1.2" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" version="1.2" xsi:schemaLocation="urn:oasis:names:tc:xliff:document:1.2 xliff-core-1.2-transitional.xsd">
   <file datatype="xml" source-language="en" original="../Resources.resx" target-language="pt-BR">
     <body>
+      <trans-unit id="CouldNotFindTesthost">
+        <source>Could not find testhost for test source '{0}'.
+
+Verify that:
+  - The test project references the 'Microsoft.NET.Test.Sdk' NuGet package.
+  - The project has been built and the output is in '{1}'.
+  - The project's target framework matches the installed .NET runtime.
+</source>
+        <target state="new">Could not find testhost for test source '{0}'.
+
+Verify that:
+  - The test project references the 'Microsoft.NET.Test.Sdk' NuGet package.
+  - The project has been built and the output is in '{1}'.
+  - The project's target framework matches the installed .NET runtime.
+</target>
+        <note>'{0}' is the path to the test source (DLL/EXE), '{1}' is the directory where testhost was searched.</note>
+      </trans-unit>
       <trans-unit id="MultipleFileVersions">
         <source>Multiple versions of same extension found. Selecting the highest version.
 {0}</source>

diff --git a/src/Microsoft.TestPlatform.TestHostProvider/Resources/xlf/Resources.ru.xlf b/src/Microsoft.TestPlatform.TestHostProvider/Resources/xlf/Resources.ru.xlf
@@ -2,6 +2,23 @@
 <xliff xmlns="urn:oasis:names:tc:xliff:document:1.2" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" version="1.2" xsi:schemaLocation="urn:oasis:names:tc:xliff:document:1.2 xliff-core-1.2-transitional.xsd">
   <file datatype="xml" source-language="en" original="../Resources.resx" target-language="ru">
     <body>
+      <trans-unit id="CouldNotFindTesthost">
+        <source>Could not find testhost for test source '{0}'.
+
+Verify that:
+  - The test project references the 'Microsoft.NET.Test.Sdk' NuGet package.
+  - The project has been built and the output is in '{1}'.
+  - The project's target framework matches the installed .NET runtime.
+</source>
+        <target state="new">Could not find testhost for test source '{0}'.
+
+Verify that:
+  - The test project references the 'Microsoft.NET.Test.Sdk' NuGet package.
+  - The project has been built and the output is in '{1}'.
+  - The project's target framework matches the installed .NET runtime.
+</target>
+        <note>'{0}' is the path to the test source (DLL/EXE), '{1}' is the directory where testhost was searched.</note>
+      </trans-unit>
       <trans-unit id="MultipleFileVersions">
         <source>Multiple versions of same extension found. Selecting the highest version.
 {0}</source>

diff --git a/src/Microsoft.TestPlatform.TestHostProvider/Resources/xlf/Resources.tr.xlf b/src/Microsoft.TestPlatform.TestHostProvider/Resources/xlf/Resources.tr.xlf
@@ -2,6 +2,23 @@
 <xliff xmlns="urn:oasis:names:tc:xliff:document:1.2" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" version="1.2" xsi:schemaLocation="urn:oasis:names:tc:xliff:document:1.2 xliff-core-1.2-transitional.xsd">
   <file datatype="xml" source-language="en" original="../Resources.resx" target-language="tr">
     <body>
+      <trans-unit id="CouldNotFindTesthost">
+        <source>Could not find testhost for test source '{0}'.
+
+Verify that:
+  - The test project references the 'Microsoft.NET.Test.Sdk' NuGet package.
+  - The project has been built and the output is in '{1}'.
+  - The project's target framework matches the installed .NET runtime.
+</source>
+        <target state="new">Could not find testhost for test source '{0}'.
+
+Verify that:
+  - The test project references the 'Microsoft.NET.Test.Sdk' NuGet package.
+  - The project has been built and the output is in '{1}'.
+  - The project's target framework matches the installed .NET runtime.
+</target>
+        <note>'{0}' is the path to the test source (DLL/EXE), '{1}' is the directory where testhost was searched.</note>
+      </trans-unit>
       <trans-unit id="MultipleFileVersions">
         <source>Multiple versions of same extension found. Selecting the highest version.
 {0}</source>

diff --git a/src/Microsoft.TestPlatform.TestHostProvider/Resources/xlf/Resources.zh-Hans.xlf b/src/Microsoft.TestPlatform.TestHostProvider/Resources/xlf/Resources.zh-Hans.xlf
@@ -2,6 +2,23 @@
 <xliff xmlns="urn:oasis:names:tc:xliff:document:1.2" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" version="1.2" xsi:schemaLocation="urn:oasis:names:tc:xliff:document:1.2 xliff-core-1.2-transitional.xsd">
   <file datatype="xml" source-language="en" original="../Resources.resx" target-language="zh-Hans">
     <body>
+      <trans-unit id="CouldNotFindTesthost">
+        <source>Could not find testhost for test source '{0}'.
+
+Verify that:
+  - The test project references the 'Microsoft.NET.Test.Sdk' NuGet package.
+  - The project has been built and the output is in '{1}'.
+  - The project's target framework matches the installed .NET runtime.
+</source>
+        <target state="new">Could not find testhost for test source '{0}'.
+
+Verify that:
+  - The test project references the 'Microsoft.NET.Test.Sdk' NuGet package.
+  - The project has been built and the output is in '{1}'.
+  - The project's target framework matches the installed .NET runtime.
+</target>
+        <note>'{0}' is the path to the test source (DLL/EXE), '{1}' is the directory where testhost was searched.</note>
+      </trans-unit>
       <trans-unit id="MultipleFileVersions">
         <source>Multiple versions of same extension found. Selecting the highest version.
 {0}</source>

diff --git a/src/Microsoft.TestPlatform.TestHostProvider/Resources/xlf/Resources.zh-Hant.xlf b/src/Microsoft.TestPlatform.TestHostProvider/Resources/xlf/Resources.zh-Hant.xlf
@@ -2,6 +2,23 @@
 <xliff xmlns="urn:oasis:names:tc:xliff:document:1.2" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" version="1.2" xsi:schemaLocation="urn:oasis:names:tc:xliff:document:1.2 xliff-core-1.2-transitional.xsd">
   <file datatype="xml" source-language="en" original="../Resources.resx" target-language="zh-Hant">
     <body>
+      <trans-unit id="CouldNotFindTesthost">
+        <source>Could not find testhost for test source '{0}'.
+
+Verify that:
+  - The test project references the 'Microsoft.NET.Test.Sdk' NuGet package.
+  - The project has been built and the output is in '{1}'.
+  - The project's target framework matches the installed .NET runtime.
+</source>
+        <target state="new">Could not find testhost for test source '{0}'.
+
+Verify that:
+  - The test project references the 'Microsoft.NET.Test.Sdk' NuGet package.
+  - The project has been built and the output is in '{1}'.
+  - The project's target framework matches the installed .NET runtime.
+</target>
+        <note>'{0}' is the path to the test source (DLL/EXE), '{1}' is the directory where testhost was searched.</note>
+      </trans-unit>
       <trans-unit id="MultipleFileVersions">
         <source>Multiple versions of same extension found. Selecting the highest version.
 {0}</source>

diff --git a/test/Microsoft.TestPlatform.TestHostProvider.UnitTests/Hosting/DotnetTestHostManagerTests.cs b/test/Microsoft.TestPlatform.TestHostProvider.UnitTests/Hosting/DotnetTestHostManagerTests.cs
@@ -543,6 +543,23 @@ public void GetTestHostProcessStartInfoShouldThrowExceptionWhenDotnetIsNotInstal
         Assert.ThrowsExactly<TestPlatformException>(action);
     }
 
+    [TestMethod]
+    public void GetTestHostProcessStartInfoShouldIncludeSourcePathInExceptionMessageWhenTesthostNotFound()
+    {
+        var sourcePath = Path.Combine(_temp, "mytest.dll");
+        var sourceDirectory = Path.GetDirectoryName(sourcePath)!;
+
+        // Ensure no testhost.dll exists anywhere
+        _mockFileHelper.Setup(fh => fh.Exists(It.IsAny<string>())).Returns(false);
+
+        Action action = () => _dotnetHostManager.GetTestHostProcessStartInfo(new[] { sourcePath }, null, _defaultConnectionInfo);
+
+        var exception = Assert.ThrowsExactly<TestPlatformException>(action);
+        Assert.Contains(sourcePath, exception.Message);
+        Assert.Contains(sourceDirectory, exception.Message);
+    }
+
+
     [TestMethod]
     public void GetTestHostProcessStartInfoShouldIncludeSourceDirectoryAsWorkingDirectory()
     {