TST: reduce number of norm comparisons (pandas-dev#45809)

Author: Andy-Grigg

pandas/tests/plotting/frame/test_frame.py

@@ -804,8 +804,7 @@ def test_plot_scatter_without_norm(self):
         ax = df.plot.scatter(x="a", y="b", c="c")
         color_min_max = (df.c.min(), df.c.max())
         default_norm = mpl.colors.Normalize(*color_min_max)
-        for c in range(100):
-            assert ax.collections[0].norm(c) == default_norm(c)
+        assert all(df.c.apply(lambda x: ax.collections[0].norm(x) == default_norm(x)))
 
     def test_plot_bar(self):
         df = DataFrame(