Add ERRORs check to AbstractOutOfBlockModificationTest

idea/testData/codeInsight/outOfBlock/InClassInUninitializedPropertyAccessor.kt

@@ -0,0 +1,11 @@
+// OUT_OF_CODE_BLOCK: FALSE
+// TYPE: '//'
+// ERROR: Property must be initialized
+
+class InClassInUninitializedPropertyAccessor {
+    var prop1: Int
+        set(value) {
+            <caret> println("prop.setter")
+            field = value
+        }
+}