More robust unit testing with both elements and measure

[chshersh]

Currently unit tests compare two treaps only by comparing elements via toList function. It would be more robust to test also the measure of the Treap. But for that we need more convenient util functions.

[sphaso]

Do you have any idea regarding this? would it be enough to map through the Treap, taking the measures and comparing the list of measures?

[chshersh]

@sphaso Sure, I have an idea. Currently unit tests for the update and construction functions look like this:

https://github.com/chshersh/treap/blob/8ff56e8dfeec056f15aa748aea487557e2b9f855/test/Test/Rand/Update.hs#L35-L36

What would be nice is to write the tests in the following form:

it "delete 0 removes first element" $
    Treap.delete 0 smallTreap `describedAs` [2..5] `with` 14

In order to make this work we need to add several custom functions to the Test.Common module, specifically:

with :: [a] -> m -> ([a], m)
with = (,)

describedAs :: Treap m a -> ([a], m) -> Expectation

(the constraints and fixities are to figure out)

[sphaso]

@chshersh great. I'm working on it on my fork. Do you think these types are good or should they be more generic?

with :: [Int] -> Int -> ([Int], Sum Int)
describedAs :: TestTreap -> ([Int], Sum Int) -> Bool

[chshersh]

@sphaso Almost correct. But instead of Bool, describedAs should have result type Expectation from the hspec library and implemented in terms of shouldBe

[sphaso]

@chshersh gotcha, I completely missed the Expectation type :) I opened a PR.