- raise exception for num_null_samples zero or negative

- add appropriate test cases

Author: thegialeo

bayesflow/diagnostics/metrics/mmd_hypothesis_test.py

@@ -78,6 +78,7 @@ def compute_mmd_hypothesis_test_from_summaries(
     ValueError
         - If number of reference summaries is less than number of observed summaries.
         - If the shapes of observed and reference summaries do not match on dimensions besides the first one.
+        - If number of null samples is less than or equal to 0.
     """
     num_observed: int = observed_summaries.shape[0]
     num_reference: int = reference_summaries.shape[0]
@@ -94,6 +95,9 @@ def compute_mmd_hypothesis_test_from_summaries(
             f"but got {observed_summaries.shape[1:]} != {reference_summaries.shape[1:]}."
         )
 
+    if num_null_samples <= 0:
+        raise ValueError(f"Number of null samples must be greater than 0, but got {num_null_samples}.")
+
     observed_summaries_tensor: Tensor = convert_to_tensor(observed_summaries, dtype="float32")
     reference_summaries_tensor: Tensor = convert_to_tensor(reference_summaries, dtype="float32")
 

tests/test_diagnostics/test_diagnostics_metrics.py

@@ -147,8 +147,9 @@ def test_compute_hypothesis_test_from_summaries_mismatched_shapes():
         )
 
 
-def test_compute_hypothesis_test_from_summaries_observed_larger_than_reference_summaries():
-    """Test that compute_hypothesis_test_from_summaries raises ValueError if observed is larger than reference."""
+def test_compute_hypothesis_test_from_summaries_reference_smaller_than_observed_summaries():
+    """Test that compute_hypothesis_test_from_summaries raises ValueError if number of reference summaries smaller than
+    observed."""
     observed_summaries = np.random.rand(20, 5)
     reference_summaries = np.random.rand(10, 5)
     num_null_samples = 10
@@ -159,6 +160,30 @@ def test_compute_hypothesis_test_from_summaries_observed_larger_than_reference_s
         )
 
 
+def test_compute_hypothesis_test_from_summaries_num_null_samples_zero():
+    """Test that compute_hypothesis_test_from_summaries raises ValueError if num_null_samples is zero."""
+    observed_summaries = np.random.rand(20, 5)
+    reference_summaries = np.random.rand(10, 5)
+    num_null_samples = 0
+
+    with pytest.raises(ValueError):
+        bf.diagnostics.metrics.compute_mmd_hypothesis_test_from_summaries(
+            observed_summaries, reference_summaries, num_null_samples
+        )
+
+
+def test_compute_hypothesis_test_from_summaries_num_null_samples_negative():
+    """Test that compute_hypothesis_test_from_summaries raises ValueError if num_null_samples is negative."""
+    observed_summaries = np.random.rand(20, 5)
+    reference_summaries = np.random.rand(10, 5)
+    num_null_samples = -1
+
+    with pytest.raises(ValueError):
+        bf.diagnostics.metrics.compute_mmd_hypothesis_test_from_summaries(
+            observed_summaries, reference_summaries, num_null_samples
+        )
+
+
 @pytest.mark.parametrize(
     "summary_network, is_true_approximator",
     [(lambda data: data + 1, True), (None, True), (lambda data: data + 1, False)],