Are there sanity check assertions?

[alexander-soare]

If I want to assert that something is working correctly within the context of my tests, rather than something working correctly in the context of the code that I'm testing, is there a special way to make that sort assertion?

An example. I wish to check that an image is being resized with "inter-area" interpolation for smaller-than-1 resize factors, and "bicubic" interpolation for 1-or-larger resize factors. I could write my test function like:

def test():
  image = # a blank image
  assert(resize_with_auto_interpolation(image, factor=2) == resize(image, factor=2, interpolation='bicubic')
  assert(resize_with_auto_interpolation(image, factor=0.5) == resize(image, factor50.4, interpolation='inter-area')

But this is a bad test because a blank image would give the same result either way.

Now a better way might be:

def test():
  image = # an image with horizontal stripes
  assert(resize_with_auto_interpolation(image, factor=2) == resize(image, factor=2, interpolation='bicubic')
  assert(resize_with_auto_interpolation(image, factor=0.5) == resize(image, factor50.4, interpolation='inter-area')

Which might work but it's not obvious that it definitely will. The developer should check that it does. They can check manually and write a comment saying that they checked. Or better, they can do sanity checks:

def test():
  image = # an image with horizontal stripes
  assert(resize_with_auto_interpolation(image, factor=2) == resize(image, factor=2, interpolation='bicubic')
  assert(resize_with_auto_interpolation(image, factor=0.5) == resize(image, factor50.4, interpolation='inter-area')

  # Sanity checks
  assert(resize_with_auto_interpolation(image, factor=2) != resize(image, factor=2, interpolation='inter-area')
  assert(resize_with_auto_interpolation(image, factor=0.5) != resize(image, factor50.4, interpolation='bicubic')

But the sanity checks are a test for the test. They are not a test for the library code. Is there a way to distinguish between the two types of assertions?

[RonnyPfannschmidt]

its unclear what you are asking for, please give a example

[alexander-soare]

Done.

[RonnyPfannschmidt]

there currently is no direct way to distinguish those, i would recommend the subtest extension to split the reporting