Add Protobuf.MSBuild.dll for tests to use

src/csharp/Grpc.Tools.Tests/IntegrationTests/TasksAssembly/readme.md

@@ -0,0 +1,5 @@
+This directory contains a copy of the DLL `Protobuf.MSBuild.dll` for custom tasks built by the Grpc.Tools project. This is required by the Grpc.Tools MSBuild targets.
+
+In the CI environment the Grpc.Tools project output is not available, thus the binary file included here.
+
+In a development environment you can rebuild and replace `Protobuf.MSBuild.dll` as necessary.

src/csharp/Grpc.Tools.Tests/MsBuildIntegrationTest.cs

@@ -189,8 +189,12 @@ namespace Grpc.Tools.Tests
             // Paths for Grpc.Tools files
             grpcToolsDir = Path.GetFullPath($"{parentDir}/../../../Grpc.Tools");
             grpcToolsBuildDir = Path.GetFullPath($"{grpcToolsDir}/build");
-            // Task assembly is needed to run the extension tasks
-            tasksAssembly = Path.GetFullPath($"{grpcToolsDir}/bin/Debug/netstandard1.3/{TASKS_ASSEMBLY_DLL}");
+
+            // Task assembly is needed to run the extension tasks.
+            // In development environments you can use this one:
+            //tasksAssembly = Path.GetFullPath($"{grpcToolsDir}/bin/Debug/netstandard1.3/{TASKS_ASSEMBLY_DLL}");
+            // This one is provided for CI environments.
+            tasksAssembly = Path.GetFullPath($"{testDataDir}/TasksAssembly/netstandard1.3/{TASKS_ASSEMBLY_DLL}");
 
             // output directory
             tempDir = Path.GetFullPath(System.IO.Path.GetTempPath()).Replace('\\','/');