Fix: Fixed a bug in regards to empty inputs in AddTextLetterByLetter class. (#3404)

* Misc: Just a class to test out some functions

* Fix: Fixed a bug in AddTextLetterByLetter class

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* Fix: Adjusted changes according to Ben's comments

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* Fix: Removed imports

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* Feat: Adjusted changes to AddTextLetterByLetter

* Feat: Added test_creation

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---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Benjamin Hackl <devel@benjamin-hackl.at>

Author: 3 people

manim/animation/creation.py

@@ -563,6 +563,11 @@ def __init__(
         **kwargs,
     ) -> None:
         self.time_per_char = time_per_char
+        # Check for empty text using family_members_with_points()
+        if not text.family_members_with_points():
+            raise ValueError(
+                f"The text mobject {text} does not seem to contain any characters."
+            )
         if run_time is None:
             # minimum time per character is 1/frame_rate, otherwise
             # the animation does not finish.

tests/module/animation/test_creation.py

@@ -0,0 +1,34 @@
+from __future__ import annotations
+
+import numpy as np
+import pytest
+
+from manim import AddTextLetterByLetter, Text, config
+
+
+def test_non_empty_text_creation():
+    """Check if AddTextLetterByLetter works for non-empty text."""
+    s = Text("Hello")
+    anim = AddTextLetterByLetter(s)
+    assert anim.mobject.text == "Hello"
+
+
+def test_empty_text_creation():
+    """Ensure ValueError is raised for empty text."""
+    with pytest.raises(ValueError, match="does not seem to contain any characters"):
+        AddTextLetterByLetter(Text(""))
+
+
+def test_whitespace_text_creation():
+    """Ensure ValueError is raised for whitespace-only text, assuming the whitespace characters have no points."""
+    with pytest.raises(ValueError, match="does not seem to contain any characters"):
+        AddTextLetterByLetter(Text("    "))
+
+
+def test_run_time_for_non_empty_text():
+    """Ensure the run_time is calculated correctly for non-empty text."""
+    s = Text("Hello")
+    run_time_per_char = 0.1
+    expected_run_time = np.max((1 / config.frame_rate, run_time_per_char)) * len(s.text)
+    anim = AddTextLetterByLetter(s, time_per_char=run_time_per_char)
+    assert anim.run_time == expected_run_time