--- a
+++ b/tests/test_selfies_utils.py
@@ -0,0 +1,123 @@
+import pytest
+
+import selfies as sf
+
+
+class Entry:
+
+    def __init__(self, selfies, symbols, label, one_hot):
+        self.selfies = selfies
+        self.symbols = symbols
+        self.label = label
+        self.one_hot = one_hot
+
+
+@pytest.fixture()
+def dataset():
+    stoi = {"[nop]": 0, "[O]": 1, ".": 2, "[C]": 3, "[F]": 4}
+    itos = {i: c for c, i in stoi.items()}
+    pad_to_len = 4
+
+    entries = [
+        Entry(selfies="",
+              symbols=[],
+              label=[0, 0, 0, 0],
+              one_hot=[[1, 0, 0, 0, 0],
+                       [1, 0, 0, 0, 0],
+                       [1, 0, 0, 0, 0],
+                       [1, 0, 0, 0, 0]]),
+        Entry(selfies="[C][C][C]",
+              symbols=["[C]", "[C]", "[C]"],
+              label=[3, 3, 3, 0],
+              one_hot=[[0, 0, 0, 1, 0],
+                       [0, 0, 0, 1, 0],
+                       [0, 0, 0, 1, 0],
+                       [1, 0, 0, 0, 0]]),
+        Entry(selfies="[C].[C]",
+              symbols=["[C]", ".", "[C]"],
+              label=[3, 2, 3, 0],
+              one_hot=[[0, 0, 0, 1, 0],
+                       [0, 0, 1, 0, 0],
+                       [0, 0, 0, 1, 0],
+                       [1, 0, 0, 0, 0]]),
+        Entry(selfies="[C][O][C][F]",
+              symbols=["[C]", "[O]", "[C]", "[F]"],
+              label=[3, 1, 3, 4],
+              one_hot=[[0, 0, 0, 1, 0],
+                       [0, 1, 0, 0, 0],
+                       [0, 0, 0, 1, 0],
+                       [0, 0, 0, 0, 1]]),
+        Entry(selfies="[C][O][C]",
+              symbols=["[C]", "[O]", "[C]"],
+              label=[3, 1, 3, 0],
+              one_hot=[[0, 0, 0, 1, 0],
+                       [0, 1, 0, 0, 0],
+                       [0, 0, 0, 1, 0],
+                       [1, 0, 0, 0, 0]])
+    ]
+
+    return entries, (stoi, itos, pad_to_len)
+
+
+@pytest.fixture()
+def dataset_flat_hots(dataset):
+    flat_hots = []
+    for entry in dataset[0]:
+        hot = [elm for vec in entry.one_hot for elm in vec]
+        flat_hots.append(hot)
+    return flat_hots
+
+
+def test_len_selfies(dataset):
+    for entry in dataset[0]:
+        assert sf.len_selfies(entry.selfies) == len(entry.symbols)
+
+
+def test_split_selfies(dataset):
+    for entry in dataset[0]:
+        assert list(sf.split_selfies(entry.selfies)) == entry.symbols
+
+
+def test_get_alphabet_from_selfies(dataset):
+    entries, (vocab_stoi, _, _) = dataset
+
+    selfies = [entry.selfies for entry in entries]
+    alphabet = sf.get_alphabet_from_selfies(selfies)
+    alphabet.add("[nop]")
+    alphabet.add(".")
+
+    assert alphabet == set(vocab_stoi.keys())
+
+
+def test_selfies_to_encoding(dataset):
+    entries, (vocab_stoi, vocab_itos, pad_to_len) = dataset
+
+    for entry in entries:
+        label, one_hot = sf.selfies_to_encoding(
+            entry.selfies, vocab_stoi, pad_to_len, "both"
+        )
+
+        assert label == entry.label
+        assert one_hot == entry.one_hot
+
+        # recover original selfies
+        selfies = sf.encoding_to_selfies(label, vocab_itos, "label")
+        selfies = selfies.replace("[nop]", "")
+        assert selfies == entry.selfies
+
+        selfies = sf.encoding_to_selfies(one_hot, vocab_itos, "one_hot")
+        selfies = selfies.replace("[nop]", "")
+        assert selfies == entry.selfies
+
+
+def test_selfies_to_flat_hot(dataset, dataset_flat_hots):
+    entries, (vocab_stoi, vocab_itos, pad_to_len) = dataset
+
+    batch = [entry.selfies for entry in entries]
+    flat_hots = sf.batch_selfies_to_flat_hot(batch, vocab_stoi, pad_to_len)
+
+    assert flat_hots == dataset_flat_hots
+
+    # recover original selfies
+    recovered = sf.batch_flat_hot_to_selfies(flat_hots, vocab_itos)
+    assert batch == [s.replace("[nop]", "") for s in recovered]