Fix test projects which reference self-contained Exes

src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.NET.Sdk.targets

@@ -1060,6 +1060,13 @@ Copyright (c) .NET Foundation. All rights reserved.
     <ShouldBeValidatedAsExecutableReference>false</ShouldBeValidatedAsExecutableReference>
   </PropertyGroup>
 
+  <PropertyGroup Condition="'$(IsTestProject)' == 'true' And '$(ValidateExecutableReferencesMatchSelfContained)' == ''">
+    <!-- Don't generate an error if a test project references a self-contained Exe.  Test projects
+         use an OutputType of Exe but will usually call APIs in a referenced Exe rather than try
+         to run it. -->
+    <ValidateExecutableReferencesMatchSelfContained>false</ValidateExecutableReferencesMatchSelfContained>
+  </PropertyGroup>
+
   <UsingTask TaskName="ValidateExecutableReferences" AssemblyFile="$(MicrosoftNETBuildTasksAssembly)" />
 
   <Target Name="ValidateExecutableReferences"

src/Tests/Microsoft.NET.Build.Tests/ReferenceExeTests.cs

@@ -259,5 +259,41 @@ public void ReferencedExeCanRunWhenPublishedWithTrimming()
 
             RunTest();
         }
+
+        [Theory]
+        [InlineData("xunit")]
+        [InlineData("mstest")]
+        public void TestProjectCanReferenceExe(string testTemplateName)
+        {
+            var testConsoleProject = new TestProject("ConsoleApp")
+            {
+                IsExe = true,
+                TargetFrameworks = "net5.0",
+                RuntimeIdentifier = EnvironmentInfo.GetCompatibleRid()
+            };
+
+            var testAsset = _testAssetsManager.CreateTestProject(testConsoleProject, identifier: testTemplateName);
+
+            var testProjectDirectory = Path.Combine(testAsset.TestRoot, "TestProject");
+            Directory.CreateDirectory(testProjectDirectory);
+
+            new DotnetCommand(Log, "new", testTemplateName)
+                .WithWorkingDirectory(testProjectDirectory)
+                .Execute()
+                .Should()
+                .Pass();
+
+            new DotnetCommand(Log, "add", "reference", ".." + Path.DirectorySeparatorChar + testConsoleProject.Name)
+                .WithWorkingDirectory(testProjectDirectory)
+                .Execute()
+                .Should()
+                .Pass();
+
+            new BuildCommand(Log, testProjectDirectory)
+                .Execute()
+                .Should()
+                .Pass();
+
+        }
     }
 }