fix and test for animator

src/textual/_animator.py

@@ -16,7 +16,7 @@ from ._types import MessageTarget
 
 if sys.version_info >= (3, 8):
     from typing import Protocol, runtime_checkable
-else:
+else:  # pragma: no cover
     from typing_extensions import Protocol, runtime_checkable
 
 
@@ -27,13 +27,13 @@ T = TypeVar("T")
 
 @runtime_checkable
 class Animatable(Protocol):
-    def blend(self: T, destination: T, factor: float) -> T:
+    def blend(self: T, destination: T, factor: float) -> T:  # pragma: no cover
         ...
 
 
 class Animation(ABC):
     @abstractmethod
-    def __call__(self, time: float) -> bool:
+    def __call__(self, time: float) -> bool:  # pragma: no cover
         raise NotImplementedError("")
 
 
@@ -45,26 +45,19 @@ class SimpleAnimation(Animation):
     duration: float
     start_value: float | Animatable
     end_value: float | Animatable
-    final_value: float | Animatable
+    final_value: object
     easing: EasingFunction
 
     def __call__(self, time: float) -> bool:
-        def blend_float(start: float, end: float, factor: float) -> float:
-            return start + (end - start) * factor
-
-        AnimatableT = TypeVar("AnimatableT", bound=Animatable)
-
-        def blend(start: AnimatableT, end: AnimatableT, factor: float) -> AnimatableT:
-            return start.blend(end, factor)
 
         if self.duration == 0:
-            value = self.end_value
+            value = self.final_value
         else:
             factor = min(1.0, (time - self.start_time) / self.duration)
             eased_factor = self.easing(factor)
 
             if factor == 1.0:
-                value = self.end_value
+                value = self.final_value
             elif isinstance(self.start_value, Animatable):
                 assert isinstance(
                     self.end_value, Animatable
@@ -88,7 +81,7 @@ class SimpleAnimation(Animation):
                         + (self.start_value - self.end_value) * eased_factor
                     )
         setattr(self.obj, self.attribute, value)
-        return value == self.end_value
+        return value == self.final_value
 
 
 class BoundAnimator:
@@ -101,7 +94,7 @@ class BoundAnimator:
         attribute: str,
         value: float,
         *,
-        final_value: Any = ...,
+        final_value: object = ...,
         duration: float | None = None,
         speed: float | None = None,
         easing: EasingFunction | str = DEFAULT_EASING,
@@ -153,7 +146,7 @@ class Animator:
         attribute: str,
         value: Any,
         *,
-        final_value: Any = ...,
+        final_value: object = ...,
         duration: float | None = None,
         speed: float | None = None,
         easing: EasingFunction | str = DEFAULT_EASING,

tests/test_animator.py

@@ -0,0 +1,166 @@
+from __future__ import annotations
+
+
+from dataclasses import dataclass
+from unittest.mock import Mock
+
+import pytest
+
+
+from textual._animator import SimpleAnimation
+
+
+class Animatable:
+    """An animatable object."""
+
+    def __init__(self, value):
+        self.value = value
+
+    def blend(self, destination: Animatable, factor: float) -> Animatable:
+        return Animatable(self.value + (destination.value - self.value) * factor)
+
+
+@dataclass
+class AnimateTest:
+    """An object to animate."""
+
+    foo: float | None = 0  # Plain float that may be set to None on final_value
+    bar: Animatable = Animatable(0)  # A mock object supporting the animatable protocol
+
+
+def test_simple_animation():
+    """Test an animation from one float to another."""
+
+    # Thing that may be animated
+    animatable = AnimateTest()
+
+    # Fake wall-clock time
+    time = 100.0
+
+    # Object that does the animation
+    animation = SimpleAnimation(
+        animatable,
+        "foo",
+        time,
+        3.0,
+        start_value=20.0,
+        end_value=50.0,
+        final_value=None,
+        easing=lambda x: x,
+    )
+
+    assert animation(time) is False
+    assert animatable.foo == 20.0
+
+    assert animation(time + 1.0) is False
+    assert animatable.foo == 30.0
+
+    assert animation(time + 2.0) is False
+    assert animatable.foo == 40.0
+
+    assert animation(time + 2.9) is False
+    assert pytest.approx(animatable.foo, 49.0)
+
+    assert animation(time + 3.0) is True  # True to indicate animation is complete
+    assert animatable.foo is None  # This is final_value
+
+    assert animation(time + 3.0) is True
+    assert animatable.foo is None
+
+
+def test_simple_animation_duration_zero():
+    """Test animation handles duration of 0."""
+
+    # Thing that may be animated
+    animatable = AnimateTest()
+
+    # Fake wall-clock time
+    time = 100.0
+
+    # Object that does the animation
+    animation = SimpleAnimation(
+        animatable,
+        "foo",
+        time,
+        0.0,
+        start_value=20.0,
+        end_value=50.0,
+        final_value=50.0,
+        easing=lambda x: x,
+    )
+
+    assert animation(time) is True
+    assert animatable.foo == 50.0
+
+    assert animation(time + 1.0) is True
+    assert animatable.foo == 50.0
+
+
+def test_simple_animation_reverse():
+    """Test an animation from one float to another, where the end value is less than the start."""
+
+    # Thing that may be animated
+    animatable = AnimateTest()
+
+    # Fake wall-clock time
+    time = 100.0
+
+    # Object that does the animation
+    animation = SimpleAnimation(
+        animatable,
+        "foo",
+        time,
+        3.0,
+        start_value=50.0,
+        end_value=20.0,
+        final_value=20.0,
+        easing=lambda x: x,
+    )
+
+    assert animation(time) is False
+    assert animatable.foo == 50.0
+
+    assert animation(time + 1.0) is False
+    assert animatable.foo == 40.0
+
+    assert animation(time + 2.0) is False
+    assert animatable.foo == 30.0
+
+    assert animation(time + 3.0) is True
+    assert animatable.foo == 20.0
+
+
+def test_animatable():
+    """Test SimpleAnimation works with the Animatable protocol"""
+
+    animatable = AnimateTest()
+
+    # Fake wall-clock time
+    time = 100.0
+
+    # Object that does the animation
+    animation = SimpleAnimation(
+        animatable,
+        "bar",
+        time,
+        3.0,
+        start_value=Animatable(20.0),
+        end_value=Animatable(50.0),
+        final_value=Animatable(50.0),
+        easing=lambda x: x,
+    )
+
+    assert animation(time) is False
+    assert animatable.bar.value == 20.0
+
+    assert animation(time + 1.0) is False
+    assert animatable.bar.value == 30.0
+
+    assert animation(time + 2.0) is False
+    assert animatable.bar.value == 40.0
+
+    assert animation(time + 2.9) is False
+    assert pytest.approx(animatable.bar.value, 49.0)
+
+    assert animation(time + 3.0) is True  # True to indicate animation is complete
+    assert animatable.bar.value == 50.0