Add RuntimeTestMode for the coreclr interpreter

src/Microsoft.DotNet.XUnitExtensions.Shared/CoreClrConfigurationDetection.cs

@@ -22,6 +22,16 @@ public static class CoreClrConfigurationDetection
         public static bool IsTieredCompilation => string.Equals(GetEnvironmentVariableValue("TieredCompilation", "1"), "1", StringComparison.InvariantCulture);
         public static bool IsHeapVerify => string.Equals(GetEnvironmentVariableValue("HeapVerify"), "1", StringComparison.InvariantCulture);
 
+        public static bool IsInterpreterActive {
+            get {
+                if (!string.IsNullOrWhiteSpace(GetEnvironmentVariableValue("Interpreter", "")))
+                    return true;
+                if (int.TryParse(GetEnvironmentVariableValue("InterpMode", "0"), out int mode) && (mode > 0))
+                    return true;
+                return false;
+            }
+        }
+
         public static bool IsGCStress => !string.Equals(GetEnvironmentVariableValue("GCStress"), "0", StringComparison.InvariantCulture);
 
         public static bool IsAnyJitStress => IsJitStress || IsJitStressRegs || IsJitMinOpts || IsTailCallStress;

src/Microsoft.DotNet.XUnitExtensions.Shared/RuntimeTestModes.cs

@@ -44,5 +44,7 @@ public enum RuntimeTestModes
         AnyJitOptimizationStress = AnyJitStress | TieredCompilation, // Disable when any JIT non-full optimization stress mode is exercised.
 
         HeapVerify = 1 << 9, // DOTNET_HeapVerify (or COMPlus_HeapVerify) is set.
+
+        InterpreterActive = 1 << 10, // DOTNET_Interpreter != "" or DOTNET_InterpMode != 0
     }
 }