rename acc_test to finite diff test

because that's what it is...

bfps/tools.py

@@ -164,7 +164,7 @@ def get_fornberg_coeffs(
             coeffs[-1].append(d[m][N][j])
     return np.array(coeffs).astype(np.float)
 
-def acceleration_test(
+def particle_finite_diff_test(
         c,
         m = 3,
         species = 0,

tests/base.py

@@ -34,7 +34,7 @@ import matplotlib.pyplot as plt
 
 import bfps
 from bfps import fluid_resize
-from bfps.tools import acceleration_test
+from bfps.tools import particle_finite_diff_test as acceleration_test
 
 parser = bfps.get_parser()
 parser.add_argument('--initialize', dest = 'initialize', action = 'store_true')