Addressed @matthew-brett's comments

Author: MarcCote

nibabel/streamlines/array_sequence.py

@@ -387,7 +387,7 @@ def concatenate(seqs, axis):
 
     Parameters
     ----------
-    seqs: list of :class:`ArraySequence` objects
+    seqs: iterable of :class:`ArraySequence` objects
         Sequences to concatenate.
     axis : int
         Axis along which the sequences will be concatenated.

nibabel/streamlines/tests/test_array_sequence.py

@@ -305,12 +305,12 @@ def test_concatenate():
     seq = SEQ_DATA['seq'].copy()  # In case there is in-place modification.
     seqs = [seq[:, [i]] for i in range(seq.common_shape[0])]
     new_seq = concatenate(seqs, axis=1)
+    seq._data += 100  # Modifying the 'seq' shouldn't change 'new_seq'.
     check_arr_seq(new_seq, SEQ_DATA['data'])
     assert_true(not new_seq._is_view)
 
-    seq = SEQ_DATA['seq'].copy()  # In case there is in-place modification.
+    seq = SEQ_DATA['seq']
     seqs = [seq[:, [i]] for i in range(seq.common_shape[0])]
     new_seq = concatenate(seqs, axis=0)
-
     assert_true(len(new_seq), seq.common_shape[0]*len(seq))
     assert_array_equal(new_seq._data, seq._data.T.reshape((-1, 1)))