Handling Doubles in ScalaTest

Question

I have just started using ScalaTest and I am using the following to compare two Doubles in my spec as follows:

  it should "calculate the price" in {
    val x = new X(10,10,12,1000)
    assert(x.price() === 185.92)
  }

The spec is passing even though I have put in a wrong value of 185.92 to compare against what the price function is returning (that actually returns 10.23 for the case above). I have other specs where I just compare Ints and they work as expected. But the ones involving Doubles are passing regardless. Is there another functions besides assert I should be using to compare Doubles?

EDIT:

def price () : Double

Answer 1

It looks to me like you've got an implicit instance of Equality[Double] in scope along the lines of org.scalactic.TolerantNumerics, for which the documentation is here.

The example from the doc is:

implicit val doubleEquality = TolerantNumerics.tolerantDoubleEquality(0.01)

But it looks like somebody has instantiated it with a really big tolerance value in your case.

You may also consider trying explicit tolerance by using +-:

assert(x.price() === 185.92 +- 0.01)

Answer 2

You can simply do actual shouldBe (expected +- tolerance) if using FlatSpec; other specs have similar matchers instead of shouldBe. It gives better messages in case of failures than assert, and the code is consistent with the other tests.