C#: Add test case for cs/unsynchronized-getter with spurious result.

Author: michaelnebel

csharp/ql/test/query-tests/Concurrency/SynchSetUnsynchGet/SynchSetUnsynchGet.cs

@@ -89,4 +89,25 @@ int GoodProperty4
             lock (mutex) GoodProperty3 = value;
         }
     }
+
+    // GOOD: both getter and setter are locked.
+    int? property2;
+    int? GoodProperty5
+    {
+        get
+        {
+            lock (mutex)
+            {
+                property2 ??= 0;
+                return property2;
+            }
+        }
+        set
+        {
+            lock (mutex)
+            {
+                property2 = value;
+            }
+        }
+    }
 }

csharp/ql/test/query-tests/Concurrency/SynchSetUnsynchGet/SynchSetUnsynchGet.expected

@@ -1,2 +1,3 @@
 | SynchSetUnsynchGet.cs:9:9:9:20 | BadProperty1 | Field $@ is guarded by a lock in the setter but not in the getter. | SynchSetUnsynchGet.cs:5:9:5:17 | property1 | property1 |
 | SynchSetUnsynchGet.cs:23:9:23:20 | BadProperty2 | Field $@ is guarded by a lock in the setter but not in the getter. | SynchSetUnsynchGet.cs:5:9:5:17 | property1 | property1 |
+| SynchSetUnsynchGet.cs:95:10:95:22 | GoodProperty5 | Field $@ is guarded by a lock in the setter but not in the getter. | SynchSetUnsynchGet.cs:94:10:94:18 | property2 | property2 |