Fix Process Start tests in outerloop on Unix.

Get the real user name in the test process, not the child process.  The outerloop tests are run with 'sudo'.  Which means by the time we are in the child process SUDO_USER will be set to 'root', since the parent test process was run with 'sudo'.

Fixes #26675

Author: eerhardt

src/System.Diagnostics.Process/tests/ProcessTests.Unix.cs

@@ -319,7 +319,7 @@ public void TestStartWithNonExistingUserThrows()
         [Fact]
         public void TestStartWithNormalUser()
         {
-            TestStartWithUserName();
+            TestStartWithUserName(GetCurrentRealUserName());
         }
 
         /// <summary>
@@ -331,26 +331,16 @@ public void TestStartWithNormalUser()
         [Trait(XunitConstants.Category, XunitConstants.RequiresElevation)]
         public void TestStartWithRootUser()
         {
-            RunTestAsSudo((Func<int>)TestStartWithUserName);
+            RunTestAsSudo(TestStartWithUserName, GetCurrentRealUserName());
         }
 
-        public static int TestStartWithUserName()
+        public static int TestStartWithUserName(string realUserName)
         {
+            Assert.NotNull(realUserName);
+            Assert.NotEqual("root", realUserName);
+
             using (ProcessTests testObject = new ProcessTests())
             {
-                string realUserName;
-                if (geteuid() == 0)
-                {
-                    realUserName = Environment.GetEnvironmentVariable("SUDO_USER");
-                }
-                else
-                {
-                    realUserName = Environment.UserName;
-                }
-
-                Assert.NotNull(realUserName);
-                Assert.NotEqual("root", realUserName);
-
                 using (Process p = testObject.CreateProcessPortable(GetCurrentEffectiveUserId))
                 {
                     p.StartInfo.UserName = realUserName;
@@ -374,6 +364,18 @@ public static int GetCurrentEffectiveUserId()
             return (int)geteuid();
         }
 
+        private static string GetCurrentRealUserName()
+        {
+            string realUserName = geteuid() == 0 ?
+                Environment.GetEnvironmentVariable("SUDO_USER") :
+                Environment.UserName;
+
+            Assert.NotNull(realUserName);
+            Assert.NotEqual("root", realUserName);
+
+            return realUserName;
+        }
+
         /// <summary>
         /// Tests when running as root and starting a new process as a normal user,
         /// the new process can't elevate back to root.
@@ -383,18 +385,16 @@ public static int GetCurrentEffectiveUserId()
         [Trait(XunitConstants.Category, XunitConstants.RequiresElevation)]
         public void TestStartWithRootUserCannotElevate()
         {
-            RunTestAsSudo((Func<int>)TestStartWithUserNameCannotElevate);
+            RunTestAsSudo(TestStartWithUserNameCannotElevate, GetCurrentRealUserName());
         }
 
-        public static int TestStartWithUserNameCannotElevate()
+        public static int TestStartWithUserNameCannotElevate(string realUserName)
         {
+            Assert.NotNull(realUserName);
+            Assert.NotEqual("root", realUserName);
+
             using (ProcessTests testObject = new ProcessTests())
             {
-                // This test should only be called with sudo
-                string realUserName = Environment.GetEnvironmentVariable("SUDO_USER");
-                Assert.NotNull(realUserName);
-                Assert.NotEqual("root", realUserName);
-
                 using (Process p = testObject.CreateProcessPortable(SetEffectiveUserIdToRoot))
                 {
                     p.StartInfo.UserName = realUserName;
@@ -415,14 +415,14 @@ public static int SetEffectiveUserIdToRoot()
             return seteuid(0);
         }
 
-        private void RunTestAsSudo(Func<int> testMethod)
+        private void RunTestAsSudo(Func<string, int> testMethod, string arg)
         {
             RemoteInvokeOptions options = new RemoteInvokeOptions()
             {
                 Start = false,
                 RunAsSudo = true
             };
-            Process p = RemoteInvoke(testMethod, options).Process;
+            Process p = RemoteInvoke(testMethod, arg, options).Process;
             AddProcessForDispose(p);
 
             p.Start();