How to test for equality of float/double in JUnit?

Question

The assertEquals(double,double) method is justifiably deprecated. Is there an alternate and/or different approach baked into junit - or do I roll my own tiny extension

  static boolean assertEquals(double d1, double d2) {
    return Math.abs(d1 - d2) < 1e-8;
}

Read the javadoc: http://junit.sourceforge.net/javadoc/org/junit/Assert.html#assertEquals%28double,%20double,%20double%29 — JB Nizet, Aug 02 '15 at 20:13

score 10 · Accepted Answer · answered Aug 02 '15 at 20:12

10

Yes, use assertEquals(double expected, double actual, double delta) instead.

answered Aug 02 '15 at 20:12

vidit

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Thanks that's the answer i needed. – WestCoastProjects Aug 02 '15 at 20:14
Personally, I tend to think `Assert.assertThat( actual, CoreMatchers.closeTo( expected, delta ) )` is a little bit nicer to read, especially with static imports ( `assertThat( actual, closeTo( expected, delta ) )` ) - but ymmv. – Florian Schaetz Aug 02 '15 at 20:31

score 1 · Answer 2 · edited May 23 '17 at 12:08

1

In the case of JUnit, there is already made functions.

But in other type of Java code, other than JUnit Test cases, IBM has a recommendation for comparing two floats, using division rather than subtraction - this makes it easier to select an epsilon that works for all ranges of input.

if (abs(a/b - 1) < epsilon)

As for the value of epsilon, I would use 5.96e-08 as given in this Wikipedia table, or perhaps 2x that value.

(see comparing float/double values using == operator)

edited May 23 '17 at 12:08

Community

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answered Aug 02 '15 at 20:13

Valentin Montmirail

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Your added reasoning from IBM is helpful. – WestCoastProjects Aug 02 '15 at 20:15

How to test for equality of float/double in JUnit?

2 Answers2