Handle user classes with weight = 0

locust/env.py

@@ -106,6 +106,8 @@ def __init__(
 
         self._filter_tasks_by_tags()
 
+        self._remove_user_classes_with_weight_zero()
+
         # Validate there's no class with the same name but in different modules
         if len(set(user_class.__name__ for user_class in self.user_classes)) != len(self.user_classes):
             raise ValueError(
@@ -216,6 +218,19 @@ def _filter_tasks_by_tags(self):
         for user_class in self.user_classes:
             filter_tasks_by_tags(user_class, self.tags, self.exclude_tags)
 
+    def _remove_user_classes_with_weight_zero(self):
+        """
+        Remove user classes having a weight of zero.
+        """
+        if len(self.user_classes) == 0:
+            # Preserve previous behaviour that allowed no user classes to be specified.
+            return
+        filtered_user_classes = [user_class for user_class in self.user_classes if user_class.weight > 0]
+        if len(filtered_user_classes) == 0:
+            # TODO: Better exception than `ValueError`?
+            raise ValueError("There are no users with weight > 0.")
+        self.user_classes[:] = filtered_user_classes
+
     def assign_equal_weights(self):
         """
         Update the user classes such that each user runs their specified tasks with equal

locust/test/test_env.py

@@ -143,3 +143,50 @@ class MyUser5(User):
         environment.assign_equal_weights()
         u = environment.user_classes[0]
         verify_tasks(u, ["outside_task", "outside_task_2", "dict_task_1", "dict_task_2", "dict_task_3"])
+
+    def test_user_classes_with_zero_weight_are_removed(self):
+        class MyUser1(User):
+            wait_time = constant(0)
+            weight = 0
+
+            @task
+            def my_task(self):
+                pass
+
+        class MyUser2(User):
+            wait_time = constant(0)
+            weight = 1
+
+            @task
+            def my_task(self):
+                pass
+
+        environment = Environment(user_classes=[MyUser1, MyUser2])
+
+        self.assertEqual(len(environment.user_classes), 1)
+        self.assertIs(environment.user_classes[0], MyUser2)
+
+    def test_all_user_classes_with_zero_weight_raises_exception(self):
+        class MyUser1(User):
+            wait_time = constant(0)
+            weight = 0
+
+            @task
+            def my_task(self):
+                pass
+
+        class MyUser2(User):
+            wait_time = constant(0)
+            weight = 0
+
+            @task
+            def my_task(self):
+                pass
+
+        with self.assertRaises(ValueError) as e:
+            environment = Environment(user_classes=[MyUser1, MyUser2])
+
+        self.assertEqual(
+            e.exception.args[0],
+            "There are no users with weight > 0.",
+        )