(fix): test internal compress error

Author: ilan-gold

numcodecs/blosc.pyx

@@ -280,7 +280,7 @@ def compress(source, char* cname, int clevel, int shuffle=SHUFFLE,
     source_ptr = source_buffer.ptr
     nbytes = source_buffer.nbytes
     if isinstance(typesize, int):
-        if typesize < 1: # pragma: no cover
+        if typesize < 1:
             raise ValueError(f"Cannot use typesize {typesize} less than 1.")
         itemsize = typesize
     else:

numcodecs/tests/test_blosc.py

@@ -290,3 +290,9 @@ def test_typesize_explicit():
 def test_typesize_less_than_1():
     with pytest.raises(ValueError, match=r"Cannot use typesize"):
         Blosc(shuffle=Blosc.SHUFFLE, typesize=0)
+    compressor = Blosc(shuffle=Blosc.SHUFFLE)
+    # not really something that should be done in practice, but good for testing.
+    compressor.typesize = 0
+    arr = np.arange(100)
+    with pytest.raises(ValueError, match=r"Cannot use typesize"):
+        compressor.encode(arr.tobytes())