PR feedback: Make shouldfail and shouldstop properties, prevent True -> False transition

src/_pytest/main.py

@@ -548,8 +548,8 @@ class Session(nodes.Collector):
         )
         self.testsfailed = 0
         self.testscollected = 0
-        self.shouldstop: Union[bool, str] = False
+        self._shouldstop: Union[bool, str] = False
-        self.shouldfail: Union[bool, str] = False
+        self._shouldfail: Union[bool, str] = False
         self.trace = config.trace.root.get("collection")
         self._initialpaths: FrozenSet[Path] = frozenset()
         self._initialpaths_with_parents: FrozenSet[Path] = frozenset()
@@ -576,6 +576,28 @@ class Session(nodes.Collector):
             self.testscollected,
         )
 
+    @property
+    def shouldstop(self) -> Union[bool, str]:
+        return self._shouldstop
+
+    @shouldstop.setter
+    def shouldstop(self, value: Union[bool, str]) -> None:
+        """Prevent plugins from setting this to False once it has been set."""
+        if value is False and self._shouldstop:
+            return
+        self._shouldstop = value
+
+    @property
+    def shouldfail(self) -> Union[bool, str]:
+        return self._shouldfail
+
+    @shouldfail.setter
+    def shouldfail(self, value: Union[bool, str]) -> None:
+        """Prevent plugins from setting this to False once it has been set."""
+        if value is False and self._shouldfail:
+            return
+        self._shouldfail = value
+
     @property
     def startpath(self) -> Path:
         """The path from which pytest was invoked.