TST: Add test cases for swt and dwt with zero-sized inputs.

make swt raise a ValueError for consistency with the dwt case

Author: grlee77

pywt/_extensions/_swt.pyx

@@ -36,6 +36,8 @@ def swt_max_level(size_t input_len):
     multiple of ``2**n``. ``numpy.pad`` can be used to pad a signal up to an
     appropriate length as needed.
     """
+    if input_len < 1:
+        raise ValueError("Cannot apply swt to a size 0 signal.")
     max_level = common.swt_max_level(input_len)
     if max_level == 0:
         warnings.warn(

pywt/tests/test_dwt_idwt.py

@@ -223,3 +223,13 @@ def test_error_on_continuous_wavelet():
 
         cA, cD = pywt.dwt(data, 'db1')
         assert_raises(ValueError, pywt.idwt, cA, cD, cwave)
+
+
+def test_dwt_zero_size_axes():
+    # raise on empty input array
+    assert_raises(ValueError, pywt.dwt, [], 'db2')
+  
+    # >1D case uses a different code path so check there as well
+    x = np.ones((1, 4))[0:0, :]  # 2D with a size zero axis
+    assert_raises(ValueError, pywt.dwt, x, 'db2', axis=0)
+

pywt/tests/test_swt.py

@@ -525,3 +525,13 @@ def test_iswtn_mixed_dtypes():
         y = pywt.iswtn(coeffs, wav)
         assert_equal(output_dtype, y.dtype)
         assert_allclose(y, x, rtol=1e-3, atol=1e-3)
+
+
+def test_swt_zero_size_axes():
+    # raise on empty input array
+    assert_raises(ValueError, pywt.swt, [], 'db2')
+  
+    # >1D case uses a different code path so check there as well
+    x = np.ones((1, 4))[0:0, :]  # 2D with a size zero axis
+    assert_raises(ValueError, pywt.swtn, x, 'db2', level=1, axes=(0,))
+