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Maxi Contieri
Maxi Contieri

Posted on • Originally published at maximilianocontieri.com

Code Smell 108 - Float Assertions

#oop #tutorial #codenewbie #cleancode

Asserting two float numbers are the same is a very difficult problem

TL;DR: Don't compare floats

Problems

  • Wrong test results

  • Fragile tests

  • Fail fast principle violation

Solutions

  1. Avoid floats unless you have REAL performance concerns

  2. Use arbitrary precision numbers

  3. If you need to compare floats compare with tolerance.

Context

Comparing float numbers is an old computer science problem.

The usual solution is to use threshold comparisons.

We recommend avoiding floats at all and trying to use infinite precision numbers.

Sample Code

Wrong 

Assert.assertEquals(0.0012f, 0.0012f); // Deprecated
Assert.assertTrue(0.0012f == 0.0012f); // Not JUnit - Smell
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Right 

Assert.assertEquals(0.0012f, 0.0014f, 0.0002); // true
Assert.assertEquals(0.0012f, 0.0014f, 0.0001); // false
// last parameter is the delta threshold

Assert.assertEquals(12 / 10000, 12 / 10000); // true
Assert.assertEquals(12 / 10000, 14 / 10000); // false