troubleshoot test that's failing only on AppVeyor

.gitignore

@@ -14,3 +14,4 @@ TestResult.xml
 *.bak
 .idea
 lcov.info
+coverage.json

Flurl.sln

@@ -28,7 +28,12 @@ Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "build", "build", "{B6BF9238
 	ProjectSection(SolutionItems) = preProject
 		appveyor.yml = appveyor.yml
 		Build\build.cmd = Build\build.cmd
+		Build\build.sh = Build\build.sh
+		Build\Flurl.netstandard.sln = Build\Flurl.netstandard.sln
 		Build\test.cmd = Build\test.cmd
+		Build\test.coverage.cmd = Build\test.coverage.cmd
+		Build\test.coverage.sh = Build\test.coverage.sh
+		Build\test.sh = Build\test.sh
 	EndProjectSection
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "PackageTester.NET45", "PackageTesters\PackageTester.NET45\PackageTester.NET45.csproj", "{63FD500A-7449-46E6-92C3-24CE92E817C7}"

Test/Flurl.Test/Http/FlurlClientFactoryTests.cs

@@ -39,34 +39,33 @@ public void can_configure_client_from_factory() {
 	    }
 
 	    [Test]
-	    public void ConfigureClient_is_thread_safe() {
+	    public async Task ConfigureClient_is_thread_safe() {
 		    var fac = new PerHostFlurlClientFactory();
 
 		    var sequence = new List<int>();
 
 		    var task1 = Task.Run(() => fac.ConfigureClient("http://api.com", c => {
 			    sequence.Add(1);
-			    Thread.Sleep(200);
+				Thread.Sleep(200);
 			    sequence.Add(3);
 		    }));
 
-		    Thread.Sleep(50);
+		    await Task.Delay(50);
 
 			// modifies same client as task1, should get blocked until task1 is done
 		    var task2 = Task.Run(() => fac.ConfigureClient("http://api.com", c => {
 			    sequence.Add(4);
 		    }));
 
-		    Thread.Sleep(50);
+		    await Task.Delay(50);
 
 		    // modifies different client, should run immediately
 		    var task3 = Task.Run(() => fac.ConfigureClient("http://api2.com", c => {
 			    sequence.Add(2);
 		    }));
 
-
-			Task.WaitAll(task1, task2, task3);
-		    CollectionAssert.AreEqual(new[] { 1, 2, 3, 4 }, sequence);
+			await Task.WhenAll(task1, task2, task3);
+		    Assert.AreEqual("1,2,3,4", string.Join(",", sequence));
 	    }
 	}
 }