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+import pytest%0Aimport cv2%0Aimport numpy as np%0Afrom plantcv.plantcv import image_subtract%0A%0A%0Adef test_plantcv_image_subtract(test_data):%0A    # read in images%0A    img1 = cv2.imread(test_data.small_bin_img, -1)%0A    img2 = np.copy(img1)%0A    new_img = image_subtract(img1, img2)%0A    assert np.count_nonzero(new_img) == 0%0A%0A%0Adef test_plantcv_image_subtract_fail(test_data):%0A    # read in images%0A    img1 = cv2.imread(test_data.small_bin_img, -1)%0A    img2 = cv2.imread(test_data.small_rgb_img)%0A    # test%0A    with pytest.raises(RuntimeError):%0A        _ = image_subtract(gray_img1=img1, gray_img2=img2)%0A

Add image_subtract tests module