Hspec expectations for the lens stuff http://supki.github.io/hspec-expectations-lens/

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BSD2 licensed by Matvey Aksenov

hspec-expectations-lens is a set of expectations for [Hspec][hspec]
with a [lens][lens]-compatible interface

This README is a literate haskell file which contains a Hspec spec.
You can run it with `runhaskell`; result is something akin to:

% runhaskell README.lhs

- checks targets exist
- looks as deep into structure as you want
- replaces 'shouldBe'
- checks a bigger part of the structure for equality
- checks the whole structure for equality

- is the opposite of 'shouldHave'

- gets a single target verbatim
- combines multiple targets using Monoid instance

- combines multiple targets into list

- gets the first target

- performs an action and gets the first target

- looks into the 'error' call
- looks into the division by zero


We start with pragmas, module declaration, and imports we use later.

> {-# LANGUAGE ExtendedDefaultRules #-} -- this is only neccessary because we don't like annotations
> module Main (main) where
> import Control.Lens
> import Control.Exception (evaluate)
> import Control.Exception.Lens (_ErrorCall, _DivideByZero)
> import Test.Hspec.Lens
> main :: IO ()
> main = hspec $ do

hspec-expectations-lens expectations form several groups. First one contains `shouldHave`
and `shouldNotHave` combinators—they check whether a `Fold` you give them has (or doesn't have)
any targets in the structure.

> describe "shouldHave" $ do
> it "checks targets exist" $
> Right (Just (Left 'a')) `shouldHave` _Right

We can look arbitrarily deep into the structure; for instance, `_Right._Just._Left`
would also work here:

> it "looks as deep into structure as you want" $
> Right (Just (Left 'a')) `shouldHave` _Right._Just

Finally, `shouldHave` can happily be used as a replacement for a vanilla `shouldBe`.

> it "replaces 'shouldBe'" $
> Right (Just (Left 'a')) `shouldHave` _Right._Just._Left.only 'a'
> it "checks a bigger part of the structure for equality" $
> Right (Just (Left 'a')) `shouldHave` _Right._Just.only (Left 'a')
> it "checks the whole structure for equality" $
> Right (Just (Left 'a')) `shouldHave` only (Right (Just (Left 'a')))

`shouldNotHave` is the opposite of `shouldHave` as its name implies, it checks
whether a `Fold` does not have any targets in the structure.

> describe "shouldNotHave" $
> it "is the opposite of 'shouldHave'" $
> Right (Just (Left 'a')) `shouldNotHave` _Left

Next group of expectations is those of them that actually care about the result
of looking into the structure. It consists of `shouldView`, `shouldPreview`,
`shouldList`, and `shouldPerform`. They derive names from `view`, `preview`, `toListOf`,
and `perform` `combinators from the lens package.

`shouldView` works similarly to `view`, no big surprises here. If a `Fold` is actually
a `Getter`, you just get its target:

> describe "shouldView" $ do
> it "gets a single target verbatim" $
> (1, (((1, 7), 8), 2, (3, 4), 5, 7)) `shouldView` 7 `through` _2._1._1._2

(`through` is just a fancy name for `id`; it helps to avoid parentheses)

Otherwise, if `Fold` has multiple targets, they are combined using `Monoid` instance
for the target type (and it better have one):

> it "combines multiple targets using Monoid instance" $
> [("foo", 1), ("bar", 2), ("baz", 3)] `shouldView` "foobarbaz" `through` folded._1

`shouldList` is like `toListOf`, that is, it combines its targets into the list:

> describe "shouldList" $
> it "combines multiple targets into list" $
> [("foo", 1), ("bar", 2), ("baz", 3)] `shouldList` [1, 2, 3] `through` folded._2

`shouldPreview` is like `preview` in that it only cares about the first target:

> describe "shouldPreview" $
> it "gets the first target" $
> [1..10] `shouldPreview` 10 `through` reversed.folded

The last combinator, which does not really belong to any of the previous groups,
is `shouldThrow`. It uses composable selectors to determine which
exception was thrown:

> describe "shouldThrow" $ do
> it "looks into the 'error' call" $
> error "foo" `shouldThrow` _ErrorCall.only "foo"
> it "looks into the division by zero" $
> evaluate (1 `div` 0) `shouldThrow` _DivideByZero

[hspec]: http://hspec.github.io/
[lens]: https://github.com/ekmett/lens/



  • Reflect API changes in lens-4.7

  • Update to lens-4.0

  • Maintenance: Upper bound on lens

  • Add a shouldPerform expectation
  • Improve expectations' error messages

  • Add a shouldThrow expectation, a lensy variant of shouldThrow

  • Add a Test.Hspec.Lens module, re-exporting Test.Hspec with Test.Hspec.Expectations.Lens expectations

  • More documentation with fake type signatures

  • shouldHave, shouldNotHave, shouldView, shouldPreview, and shouldList
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