Fix random csproj generation

Author: jviau

test/Azure.Functions.Sdk.Tests/Integration/MSBuildSdkTestBase.cs

@@ -54,7 +54,7 @@ protected virtual void Dispose(bool disposing)
     }
 
     // Ensure this starts with a non-numeric character to be a valid csproj name.
-    protected string GetTempCsproj() => "azfunc.test." + _temp.GetRandomFile(ext: ".csproj");
+    protected string GetTempCsproj() => _temp.GetRandomCsproj();
 
     private static string GetArtifactsPath()
     {

test/Azure.Functions.Sdk.Tests/Tasks/Extensions/ResolveExtensionPackagesTests.cs

@@ -156,7 +156,7 @@ private static ResolveExtensionPackages CreateTask(
     private string RestoreProject(Action<ProjectCreator>? configure = null)
     {
         ProjectCreator project = ProjectCreator.Templates.NetCoreProject(
-            path: _temp.GetRandomFile(ext: ".csproj"), targetFramework: "net8.0", configure: configure);
+            path: _temp.GetRandomCsproj(), targetFramework: "net8.0", configure: configure);
 
         project.Restore().Should().BeSuccessful(); // use assertion to throw on failure.
         project.TryGetPropertyValue("ProjectAssetsFile", out string? value);

test/Azure.Functions.Sdk.Tests/TempDirectory.cs

@@ -15,9 +15,13 @@ public TempDirectory()
 
     public string Path { get; }
 
-    public string GetRandomFile(string? ext = null)
+    // GetRandomFileName() might start with numbers. Prefixing az.func_ to ensure it's a valid C# identifier.
+    public string GetRandomCsproj() => GetRandomFile(prefix: "az.func_", ext: ".csproj");
+
+    public string GetRandomFile(string? prefix = null, string? ext = null)
     {
-        string path = IOPath.Combine(Path, IOPath.GetRandomFileName());
+        string fileName = $"{prefix}{IOPath.GetRandomFileName()}";
+        string path = IOPath.Combine(Path, fileName);
         if (!string.IsNullOrEmpty(ext))
         {
             if (!ext.StartsWith('.'))