[Xamarin.Android.Build.Tests] Fix DesignTimeBuild Test

The test was using the global cache to store the downloaded files.
As a result if we get multiple tests/commits building at the
same time we end up deleting files half way through a test run.

So lets make use of a local cache for the test by using the
`XAMARIN_CACHEPATH` environment variable.

Author: dellis1972

src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/AndroidUpdateResourcesTest.cs

@@ -1,4 +1,4 @@
-using System;
+using System;
 using Xamarin.ProjectTools;
 using NUnit.Framework;
 using System.Linq;
@@ -37,14 +37,19 @@ public void RepetitiveBuild ()
 		[Test]
 		public void DesignTimeBuild ([Values(false, true)] bool isRelease)
 		{
+			var path = Path.Combine (Root, "temp", $"DesignTimeBuild_{isRelease}");
+			var cachePath = Path.Combine (path, "Cache");
+			var envVar = new Dictionary<string, string> () {
+				{ "XAMARIN_CACHEPATH", cachePath },
+			};
 			var url = "http://dl-ssl.google.com/android/repository/build-tools_r24-macosx.zip";
 			var md5 = MD5.Create ();
 			var hash = string.Concat (md5.ComputeHash (Encoding.UTF8.GetBytes (url)).Select (b => b.ToString ("X02")));
-			var zipPath = Path.Combine (CachePath, "zips", $"{hash}.zip");
+			var zipPath = Path.Combine (cachePath, "zips", $"{hash}.zip");
 			if (File.Exists (zipPath))
 				File.Delete (zipPath);
 
-			var extractedDir = Path.Combine (CachePath, "Lib1");
+			var extractedDir = Path.Combine (cachePath, "Lib1");
 			if (Directory.Exists (extractedDir))
 				Directory.Delete (extractedDir, recursive: true);
 
@@ -65,19 +70,24 @@ public void DesignTimeBuild ([Values(false, true)] bool isRelease)
 					new BuildItem.ProjectReference (@"..\Lib1\Lib1.csproj", lib.ProjectName, lib.ProjectGuid),
 				},
 			};
-			var path = Path.Combine (Root, "temp", $"DesignTimeBuild_{isRelease}");
+			
 			using (var l = CreateDllBuilder (Path.Combine (path, lib.ProjectName))) {
 				using (var b = CreateApkBuilder (Path.Combine (path, proj.ProjectName))) {
 					l.Verbosity = LoggerVerbosity.Diagnostic;
+					Assert.IsTrue(l.Clean(lib), "Lib1 should have cleaned successfully");
 					Assert.IsTrue (l.Build (lib), "Lib1 should have built successfully");
 					b.Verbosity = LoggerVerbosity.Diagnostic;
 					b.ThrowOnBuildFailure = false;
-					Assert.IsTrue (b.UpdateAndroidResources (proj, parameters: new string [] { "DesignTimeBuild=true" }),
+					Assert.IsTrue (b.Clean(proj), "App should have cleaned successfully");
+					Assert.IsTrue (b.UpdateAndroidResources (proj, doNotCleanupOnUpdate: true, parameters: new string [] { "DesignTimeBuild=true" }, environmentVariables: envVar),
 						"first build failed");
 					Assert.IsTrue (b.LastBuildOutput.Contains ("Skipping download of "),
 						"failed to skip the downloading of files.");
-					Assert.IsTrue (b.Build (proj), "second build failed");
-					Assert.IsTrue (File.Exists (zipPath), $"Zip should have been downloaded to {zipPath}");
+					WaitFor (1000);
+					b.Target = "Build";
+					Assert.IsTrue (b.Build (proj, doNotCleanupOnUpdate: true, parameters: new string [] { "DesignTimeBuild=false" }, environmentVariables: envVar), "second build failed");
+					Assert.IsFalse(b.Output.IsTargetSkipped ("_BuildAdditionalResourcesCache"), "_BuildAdditionalResourcesCache should have run.");
+					Assert.IsTrue (b.LastBuildOutput.Contains($"Downloading {url}") || b.LastBuildOutput.Contains ($"reusing existing archive: {zipPath}"), $"{url} should have been downloaded.");
 					Assert.IsTrue (File.Exists (Path.Combine (extractedDir, "1", "content", "android-N", "aapt")), $"Files should have been extracted to {extractedDir}");
 				}
 			}

src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/Utilities/BaseTest.cs

@@ -5,6 +5,7 @@
 using Xamarin.ProjectTools;
 using NUnit.Framework;
 using System.Linq;
+using System.Threading;
 
 namespace Xamarin.Android.Build.Tests
 {
@@ -51,6 +52,12 @@ public string Root {
 			}
 		}
 
+		protected void WaitFor(int milliseconds)
+		{
+			var pause = new ManualResetEvent(false);
+			pause.WaitOne(milliseconds);
+		}
+
 		protected static string RunAdbCommand (string command, bool ignoreErrors = true)
 		{
 			string ext = Environment.OSVersion.Platform != PlatformID.Unix ? ".exe" : "";

src/Xamarin.Android.Build.Tasks/Tests/Xamarin.ProjectTools/Common/Builder.cs

@@ -3,6 +3,7 @@
 using System.Diagnostics;
 using Microsoft.Build.Framework;
 using System.Text;
+using System.Collections.Generic;
 
 namespace Xamarin.ProjectTools
 {
@@ -97,7 +98,7 @@ string GetPathFromRegistry (string valueName)
 			return null;
 		}
 
-		protected bool BuildInternal (string projectOrSolution, string target, string [] parameters = null)
+		protected bool BuildInternal (string projectOrSolution, string target, string [] parameters = null, Dictionary<string, string> environmentVariables = null)
 		{
 			string buildLogFullPath = (!string.IsNullOrEmpty (BuildLogFile))
 				? Path.GetFullPath (Path.Combine (Root, Path.GetDirectoryName (projectOrSolution), BuildLogFile))
@@ -154,7 +155,13 @@ protected bool BuildInternal (string projectOrSolution, string target, string []
 					args.AppendFormat (" /p:{0}", param);
 				}
 			}
+			if (environmentVariables != null) {
+				foreach (var kvp in environmentVariables) {
+					psi.EnvironmentVariables[kvp.Key] = kvp.Value;
+				}
+			}
 			psi.Arguments = args.ToString ();
+			
 			psi.CreateNoWindow = true;
 			psi.UseShellExecute = false;
 			psi.RedirectStandardOutput = true;

src/Xamarin.Android.Build.Tasks/Tests/Xamarin.ProjectTools/Common/ProjectBuilder.cs

@@ -54,15 +54,15 @@ public void Save (XamarinProject project, bool doNotCleanupOnUpdate = false, boo
 				project.UpdateProjectFiles (ProjectDirectory, files, doNotCleanupOnUpdate);
 		}
 
-		public bool Build (XamarinProject project, bool doNotCleanupOnUpdate = false, string [] parameters = null, bool saveProject = true)
+		public bool Build (XamarinProject project, bool doNotCleanupOnUpdate = false, string [] parameters = null, bool saveProject = true, Dictionary<string, string> environmentVariables = null)
 		{
 			Save (project, doNotCleanupOnUpdate, saveProject);
 
 			Output = project.CreateBuildOutput (this);
 
 			project.NuGetRestore (ProjectDirectory, PackagesDirectory);
 
-			bool result = BuildInternal (Path.Combine (ProjectDirectory, project.ProjectFilePath), Target, parameters);
+			bool result = BuildInternal (Path.Combine (ProjectDirectory, project.ProjectFilePath), Target, parameters, environmentVariables);
 			built_before = true;
 
 			if (CleanupAfterSuccessfulBuild)
@@ -83,12 +83,12 @@ public bool Clean (XamarinProject project, bool doNotCleanupOnUpdate = false)
 			}
 		}
 
-		public bool UpdateAndroidResources (XamarinProject project, bool doNotCleanupOnUpdate = false, string [] parameters = null)
+		public bool UpdateAndroidResources (XamarinProject project, bool doNotCleanupOnUpdate = false, string [] parameters = null, Dictionary<string, string> environmentVariables = null)
 		{
 			var oldTarget = Target;
 			Target = "UpdateAndroidResources";
 			try {
-				return Build (project, doNotCleanupOnUpdate: doNotCleanupOnUpdate, parameters: parameters);
+				return Build (project, doNotCleanupOnUpdate: doNotCleanupOnUpdate, parameters: parameters, environmentVariables: environmentVariables);
 			}
 			finally {
 				Target = oldTarget;

src/Xamarin.Android.Build.Tasks/Xamarin.Android.Common.targets

@@ -377,6 +377,12 @@ Copyright (C) 2011-2012 Xamarin. All rights reserved.
 	</PropertyGroup>
 </Target>
 
+<PropertyGroup>
+	<_BeforeBuildAdditionalResourcesCache>
+		_CreatePropertiesCache;
+	</_BeforeBuildAdditionalResourcesCache>
+</PropertyGroup>
+
 <Target Name="_BuildAdditionalResourcesCache"
 	Inputs="@(ReferencePath);@(ReferenceDependencyPaths);$(MSBuildProjectFullPath);$(NugetPackagesConfig);$(_AndroidBuildPropertiesCache)"
 	Outputs="$(_AndroidResourcePathsCache)"