def test_negative_overflow():
    im = np.array([-1, 127], dtype=np.int8)
    frequencies, bin_centers = exposure.histogram(im)
    assert_array_equal(bin_centers, np.arange(-1, 128))
    assert frequencies[0] == 1
    assert frequencies[-1] == 1
    assert_array_equal(frequencies[1:-1], 0)

def test_all_negative_image():
    im = np.array([-128, -1], dtype=np.int8)
    frequencies, bin_centers = exposure.histogram(im)
    assert_array_equal(bin_centers, np.arange(-128, 0))
    assert frequencies[0] == 1
    assert frequencies[-1] == 1
    assert_array_equal(frequencies[1:-1], 0)

 def roundtrip(self, dtype, x):
     f = NamedTemporaryFile(suffix='.tif')
     fname = f.name
     f.close()
     imsave(fname, x)
     y = imread(fname)
     assert_array_equal(x, y)