Added test case for get_arc_center()

Author: AkashKarnatak

tests/test_geometry.py

@@ -0,0 +1,7 @@
+import pytest
+import numpy as np
+from manim import Sector, ORIGIN
+
+
+def test_get_arc_center():
+    assert np.all(Sector().get_arc_center() == ORIGIN)