用HUnit测试双打的哈斯克尔相等？

Question

HUnit有没有做近似等式的方法？显然，这是失败的：

test1 = TestCase (assertEqual "Should equal" (get_scores) [(0.3, 0.3), (0.6, 0.36), (1.0, 0.3399999)])

Answer 1

注意:我不知道是否有一种正确的/官方的/公认的方法来做到这一点。

Here's assertEqual的源代码

assertEqual :: (Eq a, Show a) => String -- ^ The message prefix 
                              -> a      -- ^ The expected value 
                              -> a      -- ^ The actual value
                              -> Assertion
assertEqual preface expected actual =
  unless (actual == expected) (assertFailure msg)
 where msg = (if null preface then "" else preface ++ "\n") ++
             "expected: " ++ show expected ++ "\n but got: " ++ show actual

在此基础上，基于JUnit's function for testing double equality，我们可以以相同的风格创建我们自己的：

import Control.Monad (unless)

assertEquals ::   String  -- ^ The message prefix
               -> Double  -- ^ The maximum difference between expected and actual
               -> Double  -- ^ The expected value
               -> Double  -- ^ The actual value
               -> Assertion
assertEquals preface delta expected actual = 
  unless (abs (expected - actual) < delta) (assertFailure msg)
 where msg = ... same as above ...

Answer 2

对于浮点近似比较，有一个带有一些不错的实用工具的库：

http://hackage.haskell.org/package/ieee754

Answer 3

自从这个问题第一次被提出以来，HUnit-approx package已经发布了。

它使用隐式变量epsilon和近似相等运算符~?~，而不是~=?。

下面是一个简短的示例：

tweak :: Float -> Float
tweak x = x * 1.0001

egApproxTest  = let ?epsilon = 0.01 in
    [ "strictEqual" ~: 0 ~=? tweak 0,
      "approxEqual" ~: 2 ~?~ tweak 2 ]