在python中对实现ImageDraw的方法执行单元测试

我目前正在试验pytest模块，以便为我正在进行的项目创建单元测试。我正在尝试测试“添加点”方法，该方法基于一组像素绘制椭圆。我想做的是检查“绘制”以确保椭圆已成功创建。不幸的是，我不知道该怎么做，所以任何帮助都将不胜感激。以下是我目前的代码：

（A） TheSlicePreviewMaker.py

（B） 测试许可证预览Maker.py

---

SN：我已经分别运行了slicepreviewMaker.py来检查它生成的位图文件，因此我知道代码是有效的。我想实现的是单元测试，这样每次我都不必去检查位图。

一种方法是手动检查生成的图像，如果您觉得合适，则将其保存在测试旁边，并使用图像扩散算法（例如

ImageChops.difference

）获取一个阈值，用于确保将来的测试运行仍然绘制相同的图像

例如：

# contents of conftest.py
from PIL import ImageChops, ImageDraw, Image
import pytest
import os
import py.path
import math
import operator

def rms_diff(im1, im2):
    """Calculate the root-mean-square difference between two images
    Taken from: http://snipplr.com/view/757/compare-two-pil-images-in-python/
    """
    h1 = im1.histogram()
    h2 = im2.histogram()

    def mean_sqr(a,b):
        if not a:
            a = 0.0
        if not b:
            b = 0.0
        return (a-b)**2

    return math.sqrt(reduce(operator.add, map(mean_sqr, h1, h2))/(im1.size[0]*im1.size[1]))


class ImageDiff:
    """Fixture used to make sure code that generates images continues to do so
    by checking the difference of the genereated image against known good versions.
    """

    def __init__(self, request):
        self.directory = py.path.local(request.node.fspath.dirname) / request.node.fspath.purebasename
        self.expected_name = (request.node.name + '.png') 
        self.expected_filename = self.directory / self.expected_name

    def check(self, im, max_threshold=0.0):
        __tracebackhide__ = True
        local = py.path.local(os.getcwd()) / self.expected_name
        if not self.expected_filename.check(file=1):
            msg = '\nExpecting image at %s, but it does not exist.\n'
            msg += '-> Generating here: %s'
            im.save(str(local))
            pytest.fail(msg % (self.expected_filename, local))
        else:
            expected = Image.open(str(self.expected_filename))
            rms_value = rms_diff(im, expected)
            if rms_value > max_threshold:
                im.save(str(local))
                msg = '\nrms_value %s > max_threshold of %s.\n'
                msg += 'Obtained image saved at %s'
                pytest.fail(msg % (rms_value, max_threshold, str(local))) 

@pytest.fixture
def image_diff(request):        
    return ImageDiff(request)

def create_image():
    """ dummy code that generates an image, simulating some actual code """
    im = Image.new('RGB', (100, 100), (0, 0, 0))
    draw = ImageDraw.Draw(im)
    draw.ellipse((10, 10, 90, 90), outline=(0, 0, 255), 
                 fill=(255, 255, 255))
    return im      


def test_generated_image(image_diff):        
    im = create_image()
    image_diff.check(im) 

现在，您可以在测试中使用

image\u diff

fixture。例如：

# contents of conftest.py
from PIL import ImageChops, ImageDraw, Image
import pytest
import os
import py.path
import math
import operator

def rms_diff(im1, im2):
    """Calculate the root-mean-square difference between two images
    Taken from: http://snipplr.com/view/757/compare-two-pil-images-in-python/
    """
    h1 = im1.histogram()
    h2 = im2.histogram()

    def mean_sqr(a,b):
        if not a:
            a = 0.0
        if not b:
            b = 0.0
        return (a-b)**2

    return math.sqrt(reduce(operator.add, map(mean_sqr, h1, h2))/(im1.size[0]*im1.size[1]))


class ImageDiff:
    """Fixture used to make sure code that generates images continues to do so
    by checking the difference of the genereated image against known good versions.
    """

    def __init__(self, request):
        self.directory = py.path.local(request.node.fspath.dirname) / request.node.fspath.purebasename
        self.expected_name = (request.node.name + '.png') 
        self.expected_filename = self.directory / self.expected_name

    def check(self, im, max_threshold=0.0):
        __tracebackhide__ = True
        local = py.path.local(os.getcwd()) / self.expected_name
        if not self.expected_filename.check(file=1):
            msg = '\nExpecting image at %s, but it does not exist.\n'
            msg += '-> Generating here: %s'
            im.save(str(local))
            pytest.fail(msg % (self.expected_filename, local))
        else:
            expected = Image.open(str(self.expected_filename))
            rms_value = rms_diff(im, expected)
            if rms_value > max_threshold:
                im.save(str(local))
                msg = '\nrms_value %s > max_threshold of %s.\n'
                msg += 'Obtained image saved at %s'
                pytest.fail(msg % (rms_value, max_threshold, str(local))) 

@pytest.fixture
def image_diff(request):        
    return ImageDiff(request)

def create_image():
    """ dummy code that generates an image, simulating some actual code """
    im = Image.new('RGB', (100, 100), (0, 0, 0))
    draw = ImageDraw.Draw(im)
    draw.ellipse((10, 10, 90, 90), outline=(0, 0, 255), 
                 fill=(255, 255, 255))
    return im      


def test_generated_image(image_diff):        
    im = create_image()
    image_diff.check(im) 

第一次运行此测试时，它将失败，并有以下输出：

================================== FAILURES ===================================
____________________________ test_generated_image _____________________________

image_diff = <test_foo.ImageDiff instance at 0x029ED530>

    def test_generated_image(image_diff):
        im = create_image()
>       image_diff.check(im)
E       Failed:
E       Expecting image at X:\temp\sandbox\img-diff\test_foo\test_generated_image.png, but it does not exist.
E       -> Generating here: X:\temp\sandbox\img-diff\test_generated_image.png

===============================================================失败===================================
____________________________测试生成的图像_____________________________
图像_diff=
def测试生成的图像（图像差异）：
im=创建_图像（）
>图像差异检查（im）
E失败：
E预期图像位于X:\temp\sandbox\img diff\test\u foo\test\u generated\u image.png，但它不存在。
E->此处生成：X:\temp\sandbox\img diff\test\u generated\u image.png

然后，您可以手动检查图像，如果一切正常，将其移动到与测试文件同名的目录中，测试名称为文件名加上“.png”扩展名。从现在开始，每当测试运行时，它都会检查图像是否在可接受的范围内相似

假设您更改了代码并生成了一个稍有不同的映像，测试现在将失败，如下所示：

================================== FAILURES ===================================
____________________________ test_generated_image _____________________________

image_diff = <test_foo.ImageDiff instance at 0x02A4B788>

    def test_generated_image(image_diff):
        im = create_image()
>       image_diff.check(im)
E       Failed:
E       rms_value 2.52 > max_threshold of 0.0.
E       Obtained image saved at X:\temp\sandbox\img-diff\test_generated_image.png

test_foo.py:63: Failed
========================== 1 failed in 0.03 seconds ===========================

===============================================================失败===================================
____________________________测试生成的图像_____________________________
图像_diff=
def测试生成的图像（图像差异）：
im=创建_图像（）
>图像差异检查（im）
E失败：
E rms_值2.52>最大_阈值0.0。
E获得的图像保存在X:\temp\sandbox\img diff\test\u generated\u image.png
测试_foo.py:63:失败
=====================================1在0.03秒内失败===========================

代码需要一些润色，但应该是一个良好的开端。您可以找到此代码的版本

---

干杯，

你好，布鲁诺，谢谢你的回复。我以前从未想过这种方法。公平地说，它似乎有点冗长，但我会尝试一下，看看它如何进行。欢迎观看如何使用内置方法

ImageChops.difference

来检查两个图像是否相等，而不实现均方根差（虽然没有差分阈值）。