Ideally, this would be a single comparison, preferably using `assert_close`. (This isn't true of most of the other tests here, unfortunately). Maybe something like:

```python
from skimage.filter.edges import _mask_filter_result

expected = ~(np.tri(10, 10, -1).astype(bool) |             # mask lower
             np.tri(10, 10, -2).astype(bool).transpose())  # mask upper
expected = _mask_filter_result(expected, None)
assert_close(result, expected)
```
(You'd want to move the import to the top of the file, though.)