Enhancement: Remove redundancy in FunctionGraph arguments (#1018)

* Fix x_min, x_max and color of FunctionGraph

* Add graphical unit test to FunctionGraph

* Apply review suggestions

* Pass color as argument instead of updating kwargs and run black

Author: abhijithmuthyala

manim/mobject/functions.py

@@ -119,12 +119,21 @@ def generate_points(self):
 
 
 class FunctionGraph(ParametricFunction):
-    def __init__(self, function, color=YELLOW, **kwargs):
-        self.x_min = -config["frame_x_radius"]
-        self.x_max = config["frame_x_radius"]
+    def __init__(self, function, x_min=None, x_max=None, color=YELLOW, **kwargs):
+        if x_min is None:
+            x_min = -config["frame_x_radius"]
+        if x_max is None:
+            x_max = config["frame_x_radius"]
+        self.x_min = x_min
+        self.x_max = x_max
         self.parametric_function = lambda t: np.array([t, function(t), 0])
         ParametricFunction.__init__(
-            self, self.parametric_function, t_min=self.x_min, t_max=self.x_max, **kwargs
+            self,
+            self.parametric_function,
+            t_min=self.x_min,
+            t_max=self.x_max,
+            color=color,
+            **kwargs
         )
         self.function = function
 

tests/control_data/graphical_units_data/functions/FunctionGraphTest.npz

@@ -0,0 +1,23 @@
+import pytest
+import numpy as np
+
+from manim import *
+from ..utils.testing_utils import get_scenes_to_test
+from ..utils.GraphicalUnitTester import GraphicalUnitTester
+
+
+class FunctionGraphTest(Scene):
+    def construct(self):
+        graph = FunctionGraph(
+            lambda x: 2 * np.cos(0.5 * x), x_min=-PI, x_max=PI, color=BLUE
+        )
+        self.add(graph)
+        self.wait()
+
+
+MODULE_NAME = "functions"
+
+
+@pytest.mark.parametrize("scene_to_test", get_scenes_to_test(__name__), indirect=False)
+def test_scene(scene_to_test, tmpdir, show_diff):
+    GraphicalUnitTester(scene_to_test[1], MODULE_NAME, tmpdir).test(show_diff=show_diff)