def test_yen_blank_max(self):
     image = np.empty((5, 5), dtype=np.uint8)
     image.fill(255)
     assert threshold_yen(image) == 255

 def test_yen_binary(self):
     image = np.zeros([2, 256], dtype=np.uint8)
     image[0] = 255
     assert threshold_yen(image) < 1

 def test_yen_blank_zero(self):
     image = np.zeros((5, 5), dtype=np.uint8)
     assert threshold_yen(image) == 0

 def test_yen_float_image(self):
     image = np.float64(self.image)
     assert 2 <= threshold_yen(image) < 3

 def test_yen_arange(self):
     image = np.arange(256)
     assert threshold_yen(image) == 127

 def test_yen_negative_int(self):
     image = self.image - 2
     assert threshold_yen(image) == 0

 def test_yen(self):
     assert threshold_yen(self.image) == 2

def test_yen_coins_image_as_float():
    coins = skimage.img_as_float(data.coins())
    assert 0.43 < threshold_yen(coins) < 0.44

def test_yen_coins_image():
    coins = skimage.img_as_ubyte(data.coins())
    assert 109 < threshold_yen(coins) < 111

def test_yen_camera_image():
    camera = skimage.img_as_ubyte(data.camera())
    assert 197 < threshold_yen(camera) < 199