fixed tests

CursorLang.Tests/EndToEndTests.cs

@@ -1,6 +1,8 @@
 using System.Diagnostics;
 using System.IO;
 using System.Reflection;
+using System.Runtime.InteropServices;
+using System.Text;
 
 namespace CursorLang.Tests;
 
@@ -14,6 +16,9 @@ namespace CursorLang.Tests;
 ///
 /// If the application is already running in this session, the checks skip
 /// themselves: meddling with someone else's running instance is not their business.
+///
+/// They skip themselves where there is no desktop to show a window on either — on a
+/// build agent living as a Windows service, for one.
 /// </remarks>
 public sealed class EndToEndTests
 {
@@ -59,6 +64,16 @@ public sealed class EndToEndTests
     /// <summary>A started application that shuts down together with the check.</summary>
     private sealed class Launch : IDisposable
     {
+        private const int UOI_NAME = 2;
+        private const string InteractiveWindowStation = "WinSta0";
+
+        [DllImport("user32.dll")]
+        private static extern IntPtr GetProcessWindowStation();
+
+        [DllImport("user32.dll", CharSet = CharSet.Unicode)]
+        private static extern bool GetUserObjectInformation(IntPtr hObj, int nIndex,
+            StringBuilder pvInfo, int nLength, out int lpnLengthNeeded);
+
         private Launch(Process process) => Process = process;
 
         internal Process Process { get; }
@@ -66,6 +81,11 @@ public sealed class EndToEndTests
         /// <summary>Starts the application first — making sure the place is free.</summary>
         internal static Launch Start()
         {
+            if (!HasInteractiveDesktop())
+            {
+                Assert.Skip("There is no interactive desktop here — the application has nowhere to show its window");
+            }
+
             if (Process.GetProcessesByName("CursorLang").Length > 0)
             {
                 Assert.Skip("The application is already running — this check keeps out of someone else's run");
@@ -116,6 +136,25 @@ public sealed class EndToEndTests
             return IntPtr.Zero;
         }
 
+        /// <summary>
+        /// Whether there is a desktop here to show a window on. A service gets a
+        /// window station of its own — "Service-0x0-3e7$" and the like: a window can
+        /// be created there, yet nothing shows it. Only "WinSta0" is the interactive one.
+        /// </summary>
+        private static bool HasInteractiveDesktop()
+        {
+            IntPtr station = GetProcessWindowStation();
+            if (station == IntPtr.Zero)
+            {
+                return false;
+            }
+
+            var name = new StringBuilder(256);
+
+            return GetUserObjectInformation(station, UOI_NAME, name, name.Capacity * sizeof(char), out _)
+                   && name.ToString().Equals(InteractiveWindowStation, StringComparison.OrdinalIgnoreCase);
+        }
+
         private static string ExecutablePath()
         {
             string configured = Assembly.GetExecutingAssembly()