Fix bug in unit test for shift inversion

Limit for coordinate shift was given w.r.t absolute time instead index space.
Bug had no impact because shift was below 1 sample in either case (TODO: larger shifts).

tests/test_shift_inversion_dask.py

@@ -25,8 +25,8 @@ def test_shift_inversion_numpy():
     fsample = 1 / dt
     dxi = dx_from_x(xi)
 
-    op_np = make_shift_inverse_lagrange_numpy(order, a_mod * 1.01, max_it, tol)
-    op_da = make_shift_inverse_lagrange_dask(order, a_mod * 1.01, max_it, tol)
+    op_np = make_shift_inverse_lagrange_numpy(order, a_mod * 1.01 / dt, max_it, tol)
+    op_da = make_shift_inverse_lagrange_dask(order, a_mod * 1.01 / dt, max_it, tol)
     op_na = numpyfy_dask_multi(op_da, chunks)
 
     ai_np = op_np(dxi, fsample)

tests/test_shift_inversion_numpy.py

@@ -22,7 +22,7 @@ def test_shift_inversion_numpy():
     fsample = 1 / dt
     dxi = dx_from_x(xi)
 
-    op_np = make_shift_inverse_lagrange_numpy(order, a_mod * 1.01, max_it, tol)
+    op_np = make_shift_inverse_lagrange_numpy(order, a_mod * 1.01 / dt, max_it, tol)
 
     ai_np = op_np(dxi, fsample)