Added an ITestRunnerResolverFactory that decides on which resolver to use based on the set of parameters received.

src/Microsoft.DotNet.ProjectModel/IProjectReader.cs

@@ -0,0 +1,10 @@
+// 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.
+
+namespace Microsoft.DotNet.ProjectModel
+{
+    public interface IProjectReader
+    {
+        Project ReadProject(string projectPath, ProjectReaderSettings settings = null);
+    }
+}

src/Microsoft.DotNet.ProjectModel/ProjectReader.cs

@@ -15,7 +15,7 @@ using NuGet.Versioning;
 
 namespace Microsoft.DotNet.ProjectModel
 {
-    public class ProjectReader
+    public class ProjectReader : IProjectReader
     {
         public static bool TryGetProject(string path, out Project project, ProjectReaderSettings settings = null)
         {
@@ -63,6 +63,11 @@ namespace Microsoft.DotNet.ProjectModel
         }
 
         public static Project GetProject(string projectPath, ProjectReaderSettings settings = null)
+        {
+            return new ProjectReader().ReadProject(projectPath, settings);
+        }
+
+        public Project ReadProject(string projectPath, ProjectReaderSettings settings)
         {
             projectPath = ProjectPathHelper.NormalizeProjectFilePath(projectPath);
 
@@ -70,7 +75,7 @@ namespace Microsoft.DotNet.ProjectModel
 
             using (var stream = new FileStream(projectPath, FileMode.Open, FileAccess.Read, FileShare.Read))
             {
-                return new ProjectReader().ReadProject(stream, name, projectPath, settings);
+                return ReadProject(stream, name, projectPath, settings);
             }
         }
 

src/dotnet-test-console/BaseDotnetTestRunner.cs

@@ -35,7 +35,7 @@ namespace Microsoft.DotNet.Tools.Test
             {
                 $"--configuration",
                 dotnetTestParams.Config,
-                $"{dotnetTestParams.ProjectPath}"
+                $"{dotnetTestParams.ProjectOrAssemblyPath}"
             };
 
             // Build the test specifically for the target framework \ rid of the ProjectContext. This avoids building the project

src/dotnet-test-console/DotnetTestParams.cs

@@ -23,8 +23,9 @@ namespace Microsoft.DotNet.Tools.Test
         private CommandOption _configurationOption;
         private CommandOption _portOption;
         private CommandOption _parentProcessIdOption;
-        private CommandArgument _projectPath;
+        private CommandArgument _projectOrAssemblyPath;
         private CommandOption _noBuildOption;
+        private CommandOption _testRunner;
 
         public int? Port { get; set; }
 
@@ -38,7 +39,7 @@ namespace Microsoft.DotNet.Tools.Test
 
         public string Output { get; set; }
 
-        public string ProjectPath { get; set; }
+        public string ProjectOrAssemblyPath { get; set; }
 
         public NuGetFramework Framework { get; set; }
 
@@ -50,6 +51,10 @@ namespace Microsoft.DotNet.Tools.Test
 
         public bool Help { get; set; }
 
+        public string TestRunner { get; set; }
+
+        public bool HasTestRunner => !string.IsNullOrWhiteSpace(TestRunner);
+
         public DotnetTestParams()
         {
             _app = new CommandLineApplication(false)
@@ -69,10 +74,10 @@ namespace Microsoft.DotNet.Tools.Test
             _app.OnExecute(() =>
             {
                 // Locate the project and get the name and full path
-                ProjectPath = _projectPath.Value;
+                ProjectOrAssemblyPath = _projectOrAssemblyPath.Value;
-                if (string.IsNullOrEmpty(ProjectPath))
+                if (string.IsNullOrEmpty(ProjectOrAssemblyPath))
                 {
-                    ProjectPath = Directory.GetCurrentDirectory();
+                    ProjectOrAssemblyPath = Directory.GetCurrentDirectory();
                 }
 
                 if (_parentProcessIdOption.HasValue())
@@ -156,9 +161,16 @@ namespace Microsoft.DotNet.Tools.Test
                 CommandOptionType.SingleValue);
             _noBuildOption =
                 _app.Option("--no-build", "Do not build project before testing", CommandOptionType.NoValue);
-            _projectPath = _app.Argument(
+            _testRunner =
-                "<PROJECT>",
+                _app.Option(
-                "The project to test, defaults to the current directory. Can be a path to a project.json or a project directory.");
+                    "-t|--test-runner <TEST_RUNNER>",
+                    "Test runner to be used to run the test when an assembly to test is specified. If this option " +
+                    "is not provided, we will try to find a suitable runner collocated with the assembly",
+                    CommandOptionType.SingleValue);
+            _projectOrAssemblyPath = _app.Argument(
+                "<PROJECT OR ASSEMBLY TO TEST>",
+                "The project or assembly to test, defaults to the current directory. Can be a path to a " +
+                "project.json, to a dll or a project directory.");
         }
     }
 }

src/dotnet-test-console/TestCommand.cs

@@ -41,7 +41,7 @@ namespace Microsoft.DotNet.Tools.Test
                     RegisterForParentProcessExit(dotnetTestParams.ParentProcessId.Value);
                 }
 
-                var projectPath = GetProjectPath(dotnetTestParams.ProjectPath);
+                var projectPath = GetProjectPath(dotnetTestParams.ProjectOrAssemblyPath);
                 var runtimeIdentifiers = !string.IsNullOrEmpty(dotnetTestParams.Runtime) ?
                     new[] { dotnetTestParams.Runtime } :
                     RuntimeEnvironmentRidExtensions.GetAllCandidateRuntimeIdentifiers();

src/dotnet-test-console/TestRunners/AssemblyTestRunnerResolver.cs

@@ -9,24 +9,24 @@ namespace Microsoft.DotNet.Tools.Test
 {
     public class AssemblyTestRunnerResolver : ITestRunnerResolver
     {
-        private readonly string _assemblyUnderTestPath;
+        private readonly string _directoryOfAssemblyUnderTest;
 
         private readonly IDirectory _directory;
 
-        public AssemblyTestRunnerResolver(string assemblyUnderTestPath) :
+        public AssemblyTestRunnerResolver(string directoryOfAssemblyUnderTest) :
-            this(assemblyUnderTestPath, FileSystemWrapper.Default.Directory)
+            this(directoryOfAssemblyUnderTest, FileSystemWrapper.Default.Directory)
         {
         }
 
-        internal AssemblyTestRunnerResolver(string assemblyUnderTestPath, IDirectory directory)
+        internal AssemblyTestRunnerResolver(string directoryOfAssemblyUnderTest, IDirectory directory)
         {
-            _assemblyUnderTestPath = assemblyUnderTestPath;
+            _directoryOfAssemblyUnderTest = Path.GetDirectoryName(directoryOfAssemblyUnderTest);
             _directory = directory;
         }
 
         public string ResolveTestRunner()
         {
-            var testRunnerPath = _directory.GetFiles(_assemblyUnderTestPath, "dotnet-test-*").FirstOrDefault();
+            var testRunnerPath = _directory.GetFiles(_directoryOfAssemblyUnderTest, "dotnet-test-*").FirstOrDefault();
 
             return Path.GetFileNameWithoutExtension(testRunnerPath);
         }

src/dotnet-test-console/TestRunners/DotnetTestRunnerResolverFactory.cs

@@ -0,0 +1,47 @@
+// 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 Microsoft.DotNet.ProjectModel;
+
+namespace Microsoft.DotNet.Tools.Test
+{
+    public class DotnetTestRunnerResolverFactory
+    {
+        private readonly IProjectReader _projectReader;
+
+        public DotnetTestRunnerResolverFactory(IProjectReader projectReader)
+        {
+            _projectReader = projectReader;
+        }
+
+        public ITestRunnerResolver Create(DotnetTestParams dotnetTestParams)
+        {
+            var testRunnerResolver = dotnetTestParams.ProjectOrAssemblyPath.EndsWith(".dll") ?
+                GetAssemblyTestRunnerResolver(dotnetTestParams) :
+                GetProjectJsonTestRunnerResolver(dotnetTestParams);
+
+            return testRunnerResolver;
+        }
+
+        private ITestRunnerResolver GetAssemblyTestRunnerResolver(DotnetTestParams dotnetTestParams)
+        {
+            ITestRunnerResolver testRunnerResolver = null;
+            if (dotnetTestParams.HasTestRunner)
+            {
+                testRunnerResolver = new ParameterTestRunnerResolver(dotnetTestParams.TestRunner);
+            }
+            else
+            {
+                testRunnerResolver = new AssemblyTestRunnerResolver(dotnetTestParams.ProjectOrAssemblyPath);
+            }
+
+            return testRunnerResolver;
+        }
+
+        private ITestRunnerResolver GetProjectJsonTestRunnerResolver(DotnetTestParams dotnetTestParams)
+        {
+            var project = _projectReader.ReadProject(dotnetTestParams.ProjectOrAssemblyPath);
+            return new ProjectJsonTestRunnerResolver(project);
+        }
+    }
+}

test/dotnet-test.UnitTests/GivenATestRunnerResolverFactoryAndADotnetTestParams.cs

@@ -0,0 +1,79 @@
+// 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 FluentAssertions;
+using Microsoft.DotNet.ProjectModel;
+using Microsoft.DotNet.Tools.Test;
+using Moq;
+using Xunit;
+
+namespace Microsoft.Dotnet.Tools.Test.Tests
+{
+    public class GivenATestRunnerResolverFactoryAndADotnetTestParams
+    {
+        private const string PathToAFolder = "c:/some/path";
+        private const string PathToAnAssembly = "c:/some/path/to/assembly.dll";
+        private const string SomeTestRunner = "some test runner";
+
+        private readonly string _pathToAProjectJson = Path.Combine(PathToAFolder, "project.json");
+
+        [Fact]
+        public void It_returns_a_ProjectJsonTestRunnerResolver_when_the_path_parameter_points_to_a_project_json()
+        {
+            var dotnetTestParams = new DotnetTestParams
+            {
+                ProjectOrAssemblyPath = _pathToAProjectJson
+            };
+
+            var projectReaderMock = new Mock<IProjectReader>();
+            projectReaderMock
+                .Setup(p => p.ReadProject(dotnetTestParams.ProjectOrAssemblyPath, null))
+                .Returns(new Project());
+
+            var dotnetTestRunnerResolverFactory = new DotnetTestRunnerResolverFactory(projectReaderMock.Object);
+
+            var testRunnerResolver = dotnetTestRunnerResolverFactory.Create(dotnetTestParams);
+
+            testRunnerResolver.Should().BeOfType<ProjectJsonTestRunnerResolver>();
+        }
+
+        [Fact]
+        public void It_returns_a_ProjectJsonTestRunnerResolver_when_the_path_parameter_points_to_a_folder()
+        {
+            var dotnetTestParams = new DotnetTestParams
+            {
+                ProjectOrAssemblyPath = PathToAFolder
+            };
+
+            var projectReaderMock = new Mock<IProjectReader>();
+            projectReaderMock
+                .Setup(p => p.ReadProject(dotnetTestParams.ProjectOrAssemblyPath, null))
+                .Returns(new Project());
+
+            var dotnetTestRunnerResolverFactory = new DotnetTestRunnerResolverFactory(projectReaderMock.Object);
+
+            var testRunnerResolver = dotnetTestRunnerResolverFactory.Create(dotnetTestParams);
+
+            testRunnerResolver.Should().BeOfType<ProjectJsonTestRunnerResolver>();
+        }
+
+        [Fact]
+        public void It_returns_a_ParameterTestRunnerResolver_when_an_assembly_and_a_test_runner_are_passed()
+        {
+            var dotnetTestParams = new DotnetTestParams
+            {
+                ProjectOrAssemblyPath = PathToAnAssembly,
+                TestRunner = SomeTestRunner
+            };
+
+            var projectReaderMock = new Mock<IProjectReader>();
+
+            var dotnetTestRunnerResolverFactory = new DotnetTestRunnerResolverFactory(projectReaderMock.Object);
+
+            var testRunnerResolver = dotnetTestRunnerResolverFactory.Create(dotnetTestParams);
+
+            testRunnerResolver.Should().BeOfType<ParameterTestRunnerResolver>();
+        }
+    }
+}

test/dotnet-test.UnitTests/GivenAnAssemblyTestRunnerResolver.cs

@@ -2,6 +2,7 @@
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 
 using System.Collections.Generic;
+using System.IO;
 using System.Linq;
 using System.Text.RegularExpressions;
 using FluentAssertions;
@@ -14,20 +15,21 @@ namespace Microsoft.Dotnet.Tools.Test.Tests
 {
     public class GivenAnAssemblyTestRunnerResolver
     {
-        private const string PathToAssemblyUnderTest = "path to some assembly under test";
+        private const string DirectoryOfAssemblyUnderTest = "c:/some/path";
 
         private const string TestRunnerName = "dotnet-test-someRunner";
 
         private static readonly string TestRunnerFileName = $"{TestRunnerName}.dll";
 
         [Fact]
-        public void It_finds_the_runner_in_the_same_folder_as_the_assembly()
+        public void It_finds_the_runner_in_the_same_folder_as_the_assembly_when_the_path_passed_is_to_the_assembly()
         {
             var directoryMock = new DirectoryMock();
 
-            directoryMock.AddFile(PathToAssemblyUnderTest, TestRunnerFileName);
+            directoryMock.AddFile(DirectoryOfAssemblyUnderTest, TestRunnerFileName);
 
-            var assemblyTestRunnerResolver = new AssemblyTestRunnerResolver(PathToAssemblyUnderTest, directoryMock);
+            var pathToAssemblyUnderTest = Path.Combine(DirectoryOfAssemblyUnderTest, TestRunnerFileName);
+            var assemblyTestRunnerResolver = new AssemblyTestRunnerResolver(pathToAssemblyUnderTest, directoryMock);
 
             var testRunner = assemblyTestRunnerResolver.ResolveTestRunner();
 
@@ -39,11 +41,11 @@ namespace Microsoft.Dotnet.Tools.Test.Tests
         {
             var directoryMock = new DirectoryMock();
 
-            directoryMock.AddFile(PathToAssemblyUnderTest, TestRunnerFileName);
+            directoryMock.AddFile(DirectoryOfAssemblyUnderTest, TestRunnerFileName);
-            directoryMock.AddFile(PathToAssemblyUnderTest, "dotnet-test-someOtherTestRunner.dll");
+            directoryMock.AddFile(DirectoryOfAssemblyUnderTest, "dotnet-test-someOtherTestRunner.dll");
-            directoryMock.AddFile(PathToAssemblyUnderTest, "dotnet-test-AndYetAnotherTestRunner.dll");
+            directoryMock.AddFile(DirectoryOfAssemblyUnderTest, "dotnet-test-AndYetAnotherTestRunner.dll");
 
-            var assemblyTestRunnerResolver = new AssemblyTestRunnerResolver(PathToAssemblyUnderTest, directoryMock);
+            var assemblyTestRunnerResolver = new AssemblyTestRunnerResolver(DirectoryOfAssemblyUnderTest, directoryMock);
 
             var bestEffortTestRunner = assemblyTestRunnerResolver.ResolveTestRunner();
 
@@ -55,7 +57,7 @@ namespace Microsoft.Dotnet.Tools.Test.Tests
         {
             var directoryMock = new DirectoryMock();
 
-            var assemblyTestRunnerResolver = new AssemblyTestRunnerResolver(PathToAssemblyUnderTest, directoryMock);
+            var assemblyTestRunnerResolver = new AssemblyTestRunnerResolver(DirectoryOfAssemblyUnderTest, directoryMock);
 
             var testRunner = assemblyTestRunnerResolver.ResolveTestRunner();
 

test/dotnet-test.UnitTests/GivenThatWeWantToParseArgumentsForDotnetTest.cs

@@ -48,13 +48,13 @@ namespace Microsoft.Dotnet.Tools.Test.Tests
         [Fact]
         public void It_sets_the_project_path_current_folder_if_one_is_not_passed_in()
         {
-            _emptyDotnetTestParams.ProjectPath.Should().Be(Directory.GetCurrentDirectory());
+            _emptyDotnetTestParams.ProjectOrAssemblyPath.Should().Be(Directory.GetCurrentDirectory());
         }
 
         [Fact]
         public void It_sets_the_project_path_to_the_passed_value()
         {
-            _dotnetTestFullParams.ProjectPath.Should().Be(ProjectJson);
+            _dotnetTestFullParams.ProjectOrAssemblyPath.Should().Be(ProjectJson);
         }
 
         [Fact]