java - How to Assert Two doubles in JUnit Using assertEquals with Epsilon?

Question

assertEquals for doubles is deprecated. I found that the form with Epsilon should be used. It is because of impossible 100% strictness of doubles. But anyway I need to compare two doubles (expected and actual result), but I don't know how to do it.

At the moment my test looks like:

@Test
public void testCalcPossibleDistancePercentageCount() {
    int percentage = 100;
    assertEquals("Wrong max possible value for %" + percentage, 110.42, processor.calcPossibleValue(percentage));
    percentage = 75;
    /*corresponding assertions*/
}

Here are 3 double values I receive and which I want to check with JUnit: 110.42, 2760.5 and 10931.58. How should JUnit test look like with assertions for them? I receive them as a result of calculation in a method:

processor.calcPossibleValue(allowed_percentage){return /*Some weird formulae here*/;}

Answer 1

You need to add a fourth parameter to the assertEquals call: the threshold within which two doubles should be considered "equal". Your call should look like this:

assertEquals("Wrong max possible value for %" + percentage, 110.42,
        processor.calcPossibleValue(percentage), 0.01);

The above call would indicate that if the value returned by processor.calcPossibleValue(percentage) is within ± 0.01 of 110.42, then the two values are considered equal. You can change this value to make it as small as is necessary for your application.

See the JUnit documentation for more information.

Answer 2

Java double 使用IEEE 754 64 位格式。这种格式有 52 个尾数位。在比较 2 个值时，epsilon 应考虑预期值的大小。

例如， 0.01 可能对 110.42 有效，但如果预期值 > 2 ⁵²则无效。^{2 52}的量级太大以至于0.01 会因为精度而丢失（即只有52 位尾数位）。例如，2 ⁵² + 0.01 == 2 ⁵²。

考虑到这一点，epsilon 应该缩放到预期值。例如，期望值 ÷ 2 ^{52 - 3}或 110.42 ÷ 2 ^{52 - 3} = 1.96... x 10 ^-13。我选择了 2 ^{52 - 3}，因为这将在尾数的 3 个最低有效位中给出一个容差。

一个警告是，如果预期值为 0.0，则此公式将 epsilon 计算为 0.0，这对于特定情况可能过于严格。

另一个注意事项是不处理 NaN 和 ±∞。

Answer 3

断言已弃用

assertTrue("message like not equal ",expectedresult-actual == 0);

Answer 4

Assert.assertTrue("Not equals", expectedDouble -  actualDouble == 0);

无需涉及 epsilon 或 delta。