Add failing test

tests/requirements.txt

@@ -7,3 +7,4 @@ pytest
 pytest-cov
 pytest-doctestplus
 scipy
+sox

tests/test_transform_compose.py

@@ -7,6 +7,21 @@
 auglib.seed(0)
 
 
+def sox_transform(
+    signal: np.array,
+    sampling_rate: int,
+):
+    import sox
+
+    tfm = sox.Transformer()
+    tfm.pitch(2)
+    signal_augmented = tfm.build_array(
+        input_array=signal.squeeze(),
+        sample_rate_in=sampling_rate,
+    )
+    return signal_augmented
+
+
 @pytest.mark.parametrize("signal", [[1, 1]])
 @pytest.mark.parametrize("sampling_rate", [8000])
 @pytest.mark.parametrize(
@@ -26,6 +41,18 @@
             ],
             [2, 1, 1, 0],
         ),
+        (
+            # Include transform that returns a read-only arrary
+            # https://github.com/audeering/auglib/issues/31
+            [
+                auglib.transform.Function(sox_transform),
+                auglib.transform.WhiteNoiseGaussian(snr_db=20),
+            ],
+            [2, 1, 1, 0],
+        ),
+        # Affected transforms:
+        # Mix
+        # Tone
     ],
 )
 def test_compose(