--- a
+++ b/tests/utils/test_collections.py
@@ -0,0 +1,85 @@
+from edsnlp.utils.collections import (
+    batch_compress_dict,
+    batchify,
+    decompress_dict,
+    dl_to_ld,
+    flatten,
+    flatten_once,
+    get_deep_attr,
+    ld_to_dl,
+    multi_tee,
+    set_deep_attr,
+)
+
+
+def test_multi_tee():
+    gen = (i for i in range(10))
+    tee = multi_tee(gen)
+    items1 = [value for i, value in zip(tee, range(5))]
+    items2 = [value for i, value in zip(tee, range(5))]
+    assert items1 == items2 == [0, 1, 2, 3, 4]
+
+    # not the behavior I'd like (continue from 5 would be nice) but at least
+    # the generator is not exhausted
+    assert next(gen) == 6
+
+    assert multi_tee(items1) is items1
+
+
+def test_flatten():
+    items = [1, [2, 3], [[4, 5], 6], [[[7, 8], 9], 10]]
+    assert list(flatten_once(items)) == [1, 2, 3, [4, 5], 6, [[7, 8], 9], 10]
+    assert list(flatten(items)) == [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
+
+
+def test_dict_of_lists():
+    items = [{"a": 1, "b": 2}, {"a": 3, "b": 4}]
+    assert ld_to_dl(items) == {"a": [1, 3], "b": [2, 4]}
+    assert list(dl_to_ld({"a": [1, 3], "b": [2, 4]})) == items
+
+
+def test_dict_compression():
+    list1 = [1, 2, 3]
+    mapping1 = {"a": list1, "b": {"c": list1, "d": 4}}
+    list2 = [1, 2, 3]
+    mapping2 = {"a": list2, "b": {"c": list2, "d": 4}}
+
+    samples = [mapping1, mapping2]
+    assert list(batch_compress_dict(samples)) == [
+        {"a|b/c": [1, 2, 3], "b/d": 4},
+        {"a|b/c": [1, 2, 3], "b/d": 4},
+    ]
+
+    res = decompress_dict(
+        [
+            {"a|b/c": [1, 2, 3], "b/d": 4},
+            {"a|b/c": [1, 2, 3], "b/d": 4},
+        ]
+    )
+    assert res == {
+        "a": [[1, 2, 3], [1, 2, 3]],
+        "b": {"c": [[1, 2, 3], [1, 2, 3]], "d": [4, 4]},
+    }
+    assert res["a"] is res["b"]["c"]
+
+
+def test_batchify():
+    items = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
+    batches = list(batchify(items, 3))
+    assert len(batches) == 4
+    batches = list(batches)
+    assert batches == [[0, 1, 2], [3, 4, 5], [6, 7, 8], [9]]
+
+
+def test_deep_path():
+    class custom:
+        def __init__(self, values):
+            self.values = values
+
+    item = {"a": {"b": (0, 1), "other": custom((1, 2))}}
+    assert get_deep_attr(item, "a.b.0") == 0
+    assert get_deep_attr(item, "a.other.values.0") == 1
+    set_deep_attr(item, "a.b.1", 2)
+    set_deep_attr(item, "a.other.values.0", 1000)
+    assert item["a"]["b"] == (0, 2)
+    assert item["a"]["other"].values == (1000, 2)