diff --git a/testing/test_bit_sequence.py b/testing/test_bit_sequence.py
new file mode 100644
index 0000000..a5f7e69
--- /dev/null
+++ b/testing/test_bit_sequence.py
@@ -0,0 +1,71 @@
+import lightning as L
+import pytest
+import torch
+
+from chunkgfn.datamodules.bit_sequence import BitSequenceModule
+
+
+@pytest.mark.parametrize("num_modes", [60, 120, 240])
+@pytest.mark.parametrize("oracle_difficulty", ["medium", "hard"])
+@pytest.mark.parametrize("max_len", [32, 64, 128])
+@pytest.mark.parametrize("seed", [42, 2024, 7, 1234])
+def test_length_of_modes(
+    num_modes: int, oracle_difficulty: str, max_len: int, seed: int
+):
+    L.seed_everything(seed, workers=True)
+    env = BitSequenceModule(
+        max_len=max_len,
+        num_modes=num_modes,
+        num_train_iterations=1000,
+        num_val_iterations=100,
+        num_test_iterations=100,
+        threshold=0.9,
+        oracle_difficulty=oracle_difficulty,
+        batch_size=64,
+        sample_exact_length=True,
+    )
+    assert (
+        len(env.modes) == num_modes
+    ), f"The number of modes is not correct. You asked for {num_modes} modes, but got {len(env.modes)} modes."
+
+
+@pytest.mark.parametrize("max_len", [32, 64, 128])
+@pytest.mark.parametrize("seed", [42, 2024, 7, 1234])
+def test_invalid_actions_mask_exact_length(seed: int, max_len: int):
+    L.seed_everything(seed, workers=True)
+    env = BitSequenceModule(
+        max_len=max_len,
+        num_modes=60,
+        num_train_iterations=1000,
+        num_val_iterations=100,
+        num_test_iterations=100,
+        threshold=0.9,
+        oracle_difficulty="medium",
+        batch_size=64,
+        sample_exact_length=True,
+    )
+    s0 = env.s0.unsqueeze(0)
+    mask = env.get_invalid_actions_mask(s0)
+    assert (
+        tuple(mask.shape) == (s0.shape[0], len(env.actions))
+    ), f"Invalid mask shape is not correct. Expected {(s0.shape[0], len(env.actions))} but got {tuple(mask.shape)}."
+    expected_mask = torch.ones(len(env.actions))
+    expected_mask[0] = 0
+    expected_mask = expected_mask.unsqueeze(0)
+    assert torch.all(
+        mask == expected_mask
+    ), "Invalid mask is not correct. The <EOS> should not be allowed."
+
+    # Test for a state that is full
+    idx = torch.randint(1, len(env.atomic_tokens), (64, max_len + 1))
+    state = torch.zeros(64, max_len + 1, len(env.atomic_tokens)).scatter_(
+        2, idx.unsqueeze(-1), 1
+    )
+    state[:, -1] = env.padding_token
+    mask = env.get_invalid_actions_mask(state)
+    expected_mask = torch.ones(len(env.actions))
+    expected_mask[1:] = 0
+    expected_mask = expected_mask.unsqueeze(0)
+    assert torch.all(
+        mask == expected_mask
+    ), "Invalid mask is not correct. Only <EOS> token should be allowed."