Editing Module:ScribuntoUnit/doc (section)

=== assertWithinDelta ===

<syntaxhighlight lang="lua">
self:assertWithinDelta(expected, actual, delta, message)
</syntaxhighlight>

For two numbers, this tests whether the first is within a given distance (delta) from the second. This is useful to compare [[floating point]] numbers, which are used to represent numbers in the standard installation of Lua. (To be precise, it uses [[double-precision floating point]] numbers.) For example, on the version of Scribunto installed on the English Wikipedia, the expression <code>0.3 – 0.2 == 0.1</code> evaluates to <code>false</code>. This is because in practice, the expression <code>0.3 – 0.2</code> equals <code>0.09999999999999997780…</code> and the number <code>0.1</code> equals <code>0.10000000000000000555…</code>. The slight error between the two means that Lua does not consider them equal. Therefore, to test for equality between two floating point numbers, we should accept values within a small distance (delta) of each other, not just equal values. Note that this problem does not affect integers, which can be represented exactly using double-precision floating point numbers up to values of 2^53.

<syntaxhighlight lang="lua">
self:assertWithinDelta(0.1, calculator.subtract(0.3, 0.2), 1e-10)
</syntaxhighlight>