Add additional error-case tests.

Author: carljm

Modules/_testcapimodule.c

@@ -5243,6 +5243,21 @@ try_watch(int watcher_id, PyObject *obj) {
     return 0;
 }
 
+static int
+dict_watch_assert_error(int watcher_id, PyObject *obj, const char *fail_msg)
+{
+    if (!PyDict_Watch(watcher_id, obj)) {
+        raiseTestError("test_watch_dict", fail_msg);
+        return -1;
+    } else if (!PyErr_Occurred()) {
+        raiseTestError("test_watch_dict", "PyDict_Watch() returned error code without exception set");
+        return -1;
+    } else {
+        PyErr_Clear();
+    }
+    return 0;
+}
+
 static PyObject *
 test_watch_dict(PyObject *self, PyObject *Py_UNUSED(args))
 {
@@ -5321,23 +5336,30 @@ test_watch_dict(PyObject *self, PyObject *Py_UNUSED(args))
     Py_CLEAR(copy);
 
     Py_CLEAR(watched);
-    Py_CLEAR(unwatched);
 
     if (dict_watch_assert(9, "dealloc")) {
         return NULL;
     }
 
     // it is an error to try to watch a non-dict
-    if (!PyDict_Watch(wid, one)) {
-        raiseTestError("test_watch_dict", "PyDict_Watch() succeeded on non-dict");
+    if (dict_watch_assert_error(wid, one, "PyDict_Watch() succeeded on non-dict")) {
         return NULL;
-    } else if (!PyErr_Occurred()) {
-        raiseTestError("test_watch_dict", "PyDict_Watch() returned error code without exception set");
+    }
+
+    // It is an error to pass an out-of-range watcher ID
+    if (dict_watch_assert_error(-1, unwatched, "PyDict_Watch() succeeded on negative watcher ID")) { 
+        return NULL;
+    }
+    if (dict_watch_assert_error(8, unwatched, "PyDict_Watch() succeeded on too-large watcher ID")) {
+        return NULL;
+    }
+
+    // It is an error to pass a never-registered watcher ID
+    if (dict_watch_assert_error(7, unwatched, "PyDict_Watch() succeeded on unused watcher ID")) { 
         return NULL;
-    } else {
-        PyErr_Clear();
     }
 
+    Py_CLEAR(unwatched);
     Py_CLEAR(g_dict_watch_events);
     Py_DECREF(one);
     Py_DECREF(two);