How can I test floating-point equality using chai?

javascript floating-point precision chai
zigg picture zigg · Sep 24, 2015 · Viewed 8k times · Source

We're using Chai's BDD API to write unit tests.

How can we assert floating point equality?

For example, if I try to make this assertion to check for a 66⅔% return value:

expect(percentage).to.equal(2 / 3 * 100.0);

I get this failure:

AssertionError: expected 66.66666666666667 to equal 66.66666666666666
Expected :66.66666666666666
Actual   :66.66666666666667

Answer

GolezTrol picture GolezTrol · Jan 26, 2016

I was looking for this too, and apart from this question, I also found this discussion regarding a feature request that led to the addition of closeTo. With that you can specify a value and a +/- delta, so basically it lets you specify the precision with which to check the result.

percentage.should.be.closeTo(6.666, 0.001);

or

// `closeTo` is an alias for the arguably better name `approximately`
percentage.should.be.approximately(6.666, 0.001);

or

expect(percentage).to.be.closeTo(6.666, 0.001)

It's not perfect of course, because this will approve any number from 6.665 to 6.667.

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