clojure.test应该在一定范围内断言两个不同的浮点数相等。

Question

我使用clojure.test进行单元测试。

有些测试失败是因为非常接近的浮点数被认为是不同的。

expected: (= expected result)
  actual: (not (= 1.0 0.9999999999999998))

expected: (= expected result)
  actual: (not (= 0.5 0.4999999999999999))

我需要指示clojure.test理解(= 0.9999 1.0)是真的。

例如，使用NUnit，我可以使用Is.EqualTo().Within()来实现这一点。

Note

在我的具体例子中，1.0和0.999实际上是一回事。

Answer 1

找到一个很好的解决这个问题的方法，是很多年前我开始使用Clojure时遇到的第一个问题之一。我正是为此创建了rel=函数在图佩洛图书馆：

  (rel= val1 val2 & opts)  
  "Returns true if 2 double-precision numbers are relatively equal, 
  else false. Relative equality is specified as either (1) the N 
  most significant digits are equal, or (2) the absolute difference 
  is less than a tolerance value.  Input values are coerced to double 
  before comparison."

在这里，它正在发挥作用：

(ns tst.demo.core
  (:use demo.core tupelo.core tupelo.test))

(dotest
  (is   (rel=   123450000   123456789  :digits 4 )) ; .12345 * 10^9
  (isnt (rel=   123450000   123456789  :digits 6 ))
  (is   (rel= 0.123450000 0.123456789  :digits 4 )) ; .12345 * 1
  (isnt (rel= 0.123450000 0.123456789  :digits 6 ))

  (is   (rel=  1  1.001  :tol 0.01   )) ; :tol value is absolute error
  (isnt (rel=  1  1.001  :tol 0.0001 )))

Answer 2

我没有在clojure.test的API中看到任何东西，也不想看到其他依赖项，所以我编写了一个函数close-to

(ns floats-test
  (:require [clojure.test :refer :all]))

(defn abs
  [x]
  (max x (- x)))

(defn close-to
  [x y epsilon]
  (<= (abs (- x y)) epsilon))

(deftest floats...
  (testing "floats are equal"
    (is      (close-to 0.000000001 0.00000002  1e-7)))
  (testing "floats are equal (other direction)"
    (is      (close-to 0.000000002 0.00000001  1e-7)))
  (testing "floats aren't equal"
    (is (not (close-to 0.000000001 0.000001    1e-7))))
  (testing "floats aren't equal (other direction)"
    (is (not (close-to 0.000001    0.000000001 1e-7)))))