diff --git a/src/resspect/samples_utils.py b/src/resspect/samples_utils.py
index 3452db29..95fdc04e 100644
--- a/src/resspect/samples_utils.py
+++ b/src/resspect/samples_utils.py
@@ -46,6 +46,12 @@ def sep_samples(all_ids: np.array, n_test_val: int,
         keys are the sample names, values are the ids of
         objects in each sample.
     """
+    if n_train + 2 * n_test_val > len(all_ids):
+        raise ValueError(
+            f"Unable to draw samples of sizes {n_train}, {n_test_val}, and {n_test_val} "
+            f"from only {len(all_ids)} indices."
+        )
+
     samples = {}
     
     # separate ids for training
diff --git a/tests/resspect/test_bump.py b/tests/resspect/test_bump.py
index c6dda80f..98a6e9da 100644
--- a/tests/resspect/test_bump.py
+++ b/tests/resspect/test_bump.py
@@ -4,28 +4,50 @@
 
 import numpy as np
 import os
-import pytest
 
-from pandas import read_csv
+from resspect.bump import bump, fit_bump, protected_exponent, protected_sig
 
-from resspect import bump, fit_bump
 
+def test_protected_exponent():
+    """Test the protected_exponent() function."""
+    values = np.arange(0, 20)
+    results = protected_exponent(values)
 
-def test_bump():
-    """
-    Test the Bump function evaluation.
-    """
+    # Input values 0-10 should all return exp(x). Anything above that should
+    # return exp(10.0).
+    np.testing.assert_allclose(results[:11], np.exp(np.arange(0, 11)))
+    np.testing.assert_allclose(results[10:], [np.exp(10.0)] * 10)
+
+
+def test_protected_sig():
+    """Test the protected_sig() function."""
+    values = np.arange(-20, 10)
+    results = protected_sig(values)
+
+    expected_upper = 1.0 / (1.0 + np.exp(np.arange(10, -10, -1)))
+    expected_lower = 1.0 / (1.0 + np.exp(np.full(10, 10.0)))
+
+    # Input values [-20, -10] should return 1.0 / (1.0 + exp(10.0))
+    # and input values [-10, 10] should return 1.0 / (1.0 + exp(-x))
+    np.testing.assert_allclose(results[:10], expected_lower)
+    np.testing.assert_allclose(results[10:], expected_upper)
 
 
-    time = np.array([0])
+def test_bump():
+    """Test the Bump function evaluation."""
+    time = np.arange(-1, 5, 1)
     p1 = 0.225
     p2 = -2.5
     p3 = 0.038
-    
+
     res = bump(time, p1, p2, p3)
-    
     assert not np.isnan(res).any()
-   
+
+    # These were manually computed using the function and so this currently
+    # only will detect future changes in behavior (breakages).
+    expected = [0.86683499, 0.87300292, 0.87822063, 0.88254351, 0.88601519, 0.88866704]
+    np.testing.assert_allclose(res, expected)
+
     
 def test_fit_bump(test_data_path):
     """
diff --git a/tests/resspect/test_sample_utils.py b/tests/resspect/test_sample_utils.py
new file mode 100644
index 00000000..1bc4aebb
--- /dev/null
+++ b/tests/resspect/test_sample_utils.py
@@ -0,0 +1,52 @@
+"""Tests for sample_utils.py."""
+
+import numpy as np
+import pytest
+
+from resspect.samples_utils import sep_samples
+
+
+def test_sep_samples():
+    """Test that we can generate separate samples."""
+    all_ids = np.arange(0, 100)
+    samples = sep_samples(all_ids, n_test_val=10, n_train=50)
+    assert len(samples) == 4
+
+    # Check that each partition is the correct size and disjoint.
+    assert len(samples["train"]) == 50
+    assert len(np.unique(samples["train"])) == 50
+    all_seen = np.copy(samples["train"])
+
+    assert len(samples["val"]) == 10
+    assert len(np.unique(samples["val"])) == 10
+    all_seen = np.union1d(all_seen, samples["val"])
+    assert len(all_seen) == 60
+
+    assert len(samples["test"]) == 10
+    assert len(np.unique(samples["test"])) == 10
+    all_seen = np.union1d(all_seen, samples["test"])
+    assert len(all_seen) == 70
+
+    assert len(samples["query"]) == 30
+    assert len(np.unique(samples["query"])) == 30
+    all_seen = np.union1d(all_seen, samples["query"])
+    assert len(all_seen) == 100
+
+
+def test_sep_samples_too_many():
+    """Test that we fail if we try to generate more samples than IDs."""
+    all_ids = np.arange(0, 100)
+    with pytest.raises(ValueError):
+        samples = sep_samples(all_ids, n_test_val=50, n_train=80)
+    with pytest.raises(ValueError):
+        samples = sep_samples(all_ids, n_test_val=15, n_train=80)
+
+    # We are okay with exactly the same number of samples and IDs.
+    # But the 'query' bucket is empty
+    samples = sep_samples(all_ids, n_test_val=10, n_train=80)
+    assert len(samples) == 4
+    assert len(samples["query"]) == 0
+
+
+if __name__ == '__main__':
+    pytest.main()