dotnet test and publish failing badly when the project isn't restored.

Fixing this by checking for diagnostic errors before continuing.

Fix #2692
Fix #2942

test/dotnet-test.Tests/GivenThatWeWantToRunTests.cs

@@ -0,0 +1,29 @@
+// Copyright (c) .NET Foundation and contributors. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using System.IO;
+using Microsoft.DotNet.TestFramework;
+using Microsoft.DotNet.Tools.Test.Utilities;
+using Xunit;
+
+namespace Microsoft.Dotnet.Tools.Test.Tests
+{
+    public class GivenThatWeWantToRunTests : TestBase
+    {
+        [Fact]
+        public void It_fails_correctly_with_an_unrestored_project()
+        {
+            // NOTE: we don't say "WithLockFiles", so the project is "unrestored"
+            var instance = TestAssetsManager.CreateTestInstance(Path.Combine("ProjectsWithTests", "NetCoreAppOnlyProject"));
+
+            new DotnetTestCommand()
+                .ExecuteWithCapturedOutput(instance.TestRoot)
+                .Should()
+                .Fail()
+                .And
+                .HaveStdErrContaining("NU1009")
+                .And
+                .HaveStdErrContaining("dotnet restore");
+        }
+    }
+}