Enhance RuntimeEnvironmentHelper tests with exception safety verification

Co-authored-by: nkolev92 <[email protected]>

Author: Copilot

test/NuGet.Core.Tests/NuGet.Common.Test/RuntimeEnvironmentHelperTests.cs

@@ -52,6 +52,9 @@ public void PlatformDetection_ShouldBeExclusive()
             // Assert - Only one platform should be true
             var trueCount = (isWindows ? 1 : 0) + (isMacOS ? 1 : 0) + (isLinux ? 1 : 0);
             Assert.True(trueCount <= 1, $"Multiple platforms detected as true: Windows={isWindows}, macOS={isMacOS}, Linux={isLinux}");
+            
+            // At least one should be detected (we're running on some platform)
+            Assert.True(trueCount >= 1, $"No platform detected as true: Windows={isWindows}, macOS={isMacOS}, Linux={isLinux}");
         }
 
         [PlatformFact(Platform.Windows)]
@@ -123,5 +126,22 @@ public void IsMacOSX_OnLinux_ShouldReturnFalse()
             // Assert
             Assert.False(result);
         }
+        
+        [Fact]
+        public void IsMacOSX_ShouldNotThrowException()
+        {
+            // Arrange & Act & Assert
+            // This test specifically verifies that no first-chance exception is thrown
+            // when calling IsMacOSX on any platform, especially Windows
+            var exception = Record.Exception(() =>
+            {
+                var result = RuntimeEnvironmentHelper.IsMacOSX;
+                // Multiple calls to ensure consistency and no exceptions on repeated access
+                var result2 = RuntimeEnvironmentHelper.IsMacOSX;
+                Assert.Equal(result, result2);
+            });
+            
+            Assert.Null(exception);
+        }
     }
 }