Fix animations with zero runtime length to give a useful error instead of a broken pipe (#3491)

* Fix animation group not erroring when instantiated with an empty list

* Move error messages into Animation.begin()

* [pre-commit.ci] auto fixes from pre-commit.com hooks

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* Added tests

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Update manim/animation/animation.py

* Update manim/animation/composition.py

* Update manim/animation/animation.py

Co-authored-by: Jason Grace <[email protected]>

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Jason Grace <[email protected]>

Author: 3 people

manim/animation/animation.py

@@ -191,6 +191,10 @@ def begin(self) -> None:
         method.
 
         """
+        if self.run_time <= 0:
+            raise ValueError(
+                f"{self} has a runtime of <= 0 seconds, which cannot be rendered correctly! please set a runtime > 0"
+            )
         self.starting_mobject = self.create_starting_mobject()
         if self.suspend_mobject_updating:
             # All calls to self.mobject's internal updaters

manim/animation/composition.py

@@ -81,6 +81,15 @@ def get_all_mobjects(self) -> Sequence[Mobject]:
         return list(self.group)
 
     def begin(self) -> None:
+        if self.run_time <= 0:
+            tmp = (
+                "please set a runtime > 0"
+                if len(self.animations) != 0
+                else "Please add at least one Animation"
+            )
+            raise ValueError(
+                f"{self} has a runtime of 0 seconds. Which cannot be rendered correctly! {tmp}."
+            )
         if self.suspend_mobject_updating:
             self.group.suspend_updating()
         for anim in self.animations:

tests/module/animation/test_composition.py

@@ -169,3 +169,13 @@ def test_animationgroup_is_passing_remover_to_nested_animationgroups():
     assert sqr_animation.remover
     assert circ_animation.remover
     assert polygon_animation.remover
+
+
+def test_empty_animation_group_fails():
+    with pytest.raises(ValueError):
+        AnimationGroup().begin()
+
+
+def test_empty_animation_fails():
+    with pytest.raises(ValueError):
+        FadeIn(None, run_time=0).begin()