Enable test_memory

Author: slozier

src/core/IronPython/Runtime/Types/PythonType.cs

@@ -2498,6 +2498,7 @@ private void AddSubType(PythonType subtype) {
             }
 
             lock (_subtypesLock) {
+                _subtypes.RemoveAll(x => !x.TryGetTarget(out _)); // remove dead entries
                 _subtypes.Add(new WeakReference<PythonType>(subtype));
             }
         }

tests/IronPython.Tests/Cases/IronPythonCasesManifest.ini

@@ -65,12 +65,6 @@ Reason=New test needs to be written for new csharp version
 Ignore=true
 Reason=Assertion error
 
-[IronPython.test_memory]
-#RunCondition=NOT $(IS_POSIX)
-#Reason=Memory allocation on Mono may not match MS.NET
-Ignore=true
-Reason=Fails intermittently - https://github.com/IronLanguages/ironpython3/issues/508
-
 [IronPython.test_number]
 Timeout=300000 # 5 minute timeout - slow on macOS
 

tests/suite/test_memory.py

@@ -82,9 +82,9 @@ def setUp(self):
         from Microsoft.Scripting.Generation import Snippets
 
         self.skipMemoryCheck = Snippets.Shared.SaveSnippets or clr.GetCurrentRuntime().Configuration.DebugMode
-        self.expectedMem = 24000
 
         # account for adaptive compilation
+        self.expectedMem = 24000
         if is_cli64:
             self.expectedMem = int(self.expectedMem*1.25)