tweaks Heun test

TurTLE/test/test_Heun_p2p.py

@@ -328,7 +328,7 @@ def main():
     df = bla.get_particle_file()
     x = []
     v = []
-    for ii in range(200):
+    for ii in range(bla.parameters['niter_out']):
         x.append(df['tracers0/position/{0}'.format(ii)][()])
         v.append(df['tracers0/velocity/{0}'.format(ii)][()])
     df.close()
@@ -354,6 +354,7 @@ def main():
         f.savefig('traj.pdf')
     except ImportError:
         print('couldn\'t import matplotlib, no figure')
+    print(np.max(relative_error))
     assert(np.max(relative_error) < 1e-4)
     return None