Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Jump to bottom

clarify law testing's dependency on cats-testkit and scalatest #2245

Merged
merged 10 commits into from
May 10, 2018
Merged

clarify law testing's dependency on cats-testkit and scalatest #2245

Changes from 2 commits
Commits
Show all changes
10 commits
Select commit Hold shift + click to select a range
a8eae14
clarify law testing's dependency on cats-testkit and scalatest
kailuowang May 4, 2018
6889139
Update lawtesting.md
kailuowang May 4, 2018
5dca108
Update lawtesting.md
kailuowang May 7, 2018
b63abdf
Update lawtesting.md
kailuowang May 7, 2018
3311271
Update lawtesting.md
kailuowang May 7, 2018
329e5ae
fixing tut compilation
kailuowang May 8, 2018
a534cee
Update lawtesting.md
kailuowang May 8, 2018
8e5e758
Update lawtesting.md
kailuowang May 9, 2018
7e2f9de
Update lawtesting.md
kailuowang May 9, 2018
fd77b9c
Update lawtesting.md
kailuowang May 9, 2018
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
23 changes: 14 additions & 9 deletions docs/src/main/tut/typeclasses/lawtesting.md
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -7,23 +7,25 @@ section: "typeclasses"
# Law testing

[Laws](https://typelevel.org/cats/typeclasses.html#laws) are an important part of cats.
Cats uses `catalysts` and `discipline` to help test instances with laws.
To make things easier, cats ships with `cats-testkit`, which makes use of `catalysts` and `discipline` and exposes `CatsSuite` based on ScalaTest.
Cats uses `catalysts` and [discipline](https://github.com/typelevel/discipline) to help test instances with laws. To test type class
Copy link
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Why is catalysts relevant here?

laws from Cats against your instances, you need to add a `cats-laws` dependency.
If you are using `ScalaTests`, Cats also ships with `cats-testkit`, which exposes `CatsSuite` based on ScalaTest.


## Getting started

First up, you will need to specify dependencies on `cats-laws` and `cats-testkit` in your `build.sbt` file.
First up, you will need to specify dependencies on `cats-laws` in your `build.sbt` file (or `cats-testkit` if you
are using `ScalaTest`).
To make things easier, we'll also include the `scalacheck-shapeless` library in this tutorial, so we don't have to manually write instances for ScalaCheck's `Arbitrary`.

```scala
libraryDependencies ++= Seq(
"org.typelevel" %% "cats-laws" % "1.0.1" % Test,
"org.typelevel" %% "cats-testkit" % "1.0.1"% Test,
"org.typelevel" %% "cats-laws" % "1.1.0" % Test, //or `cats-testkit` if you are using ScalaTest
"com.github.alexarchambault" %% "scalacheck-shapeless_1.13" % "1.1.6" % Test
)
```


## Example: Testing a Functor instance

We'll begin by creating a data type and its Functor instance.
Expand All @@ -50,8 +52,8 @@ For simplicity we'll just use `Eq.fromUniversalEquals`:
implicit def eqTree[A: Eq]: Eq[Tree[A]] = Eq.fromUniversalEquals
```

Then we can begin to write our law tests. Start by creating a new class in your `test` folder and inheriting from `cats.tests.CatsSuite`.
`CatsSuite` extends the standard ScalaTest `FunSuite` as well as `Matchers`.
Then we can begin to write our law tests. If you are using `ScalaTest` you can inherit from `cats.tests.CatsSuite`
from `cats-testkit`. `CatsSuite` extends the standard ScalaTest `FunSuite` as well as `Matchers`.
Copy link
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

What do you do if you're not using ScalaTest? Not sure this helps.

Furthermore it also pulls in all of cats instances and syntax, so there's no need to import from `cats.implicits._`.

```tut:book
Expand All @@ -62,8 +64,11 @@ class TreeLawTests extends CatsSuite {
}
```

The key to testing laws is the `checkAll` function, which takes a name for your test and a Discipline ruleset.
Cats has defined rulesets for all type class laws in `cats.laws.discipline.*`.
The key to testing laws is the `checkAll` function provided by [discipline](https://github.com/typelevel/discipline),
which takes a name for your test and a Discipline ruleset.
Cats has defined rulesets for all type class laws in `cats.laws.discipline.*`. As of now, [discipline](https://github.com/typelevel/discipline) provides this helper `checkAll` only for `ScalaTest` and `Spec2`,
but it should not be hard for you to write your own `checkAll` for your test framework of choice following this
[example](https://github.com/typelevel/discipline/blob/master/shared/src/main/scala/scalatest/Discipline.scala).

So for our example we will want to import `cats.laws.discipline.FunctorTests` and call `checkAll` with it.
Before we do so, however,
Expand Down