Move Fixture[T] into a toplevel class.
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olafurpg
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November 1, 2020 10:01
Previously, FailException had some custom nice-to-have features that ComparisonFailException didn't have.
This makes the error message clearer in some cases.
Previously, MUnit had a subtyping constraint on `assertEquals(a, b)` so that it would fail to compile if `a` was not a subtype of `b`. This was a suboptimal solution because the compile error messages could become cryptic in some cases. Additionally, this API didn't integrate with other libaries like Cats that has its own `cats.Eq[A,B]` type-class. Now, MUnit uses a new `munit.Compare[A,B]` type-class for comparing values of different types. By default, MUnit provides a "universal" instance that permits comparison between all types and uses the built-in `==` method. Users can optionally enable "strict equality" by adding the compiler option `"-Xmacro-settings.munit.strictEquality"` in Scala 2. In Scala 3, we use the `Eql[A, B]` type-classes instead to determine type equality.
This is a fourth attempt at improving strict equality in MUnit `assertEquals()` assertions. * First attempt (current release version): require second argument to be a supertype of the first argument. This has the flaw that the compile error message is cryptic and that the ordering of the arguments affects compilation. * Second attempt: use `Eql[A, B]` in Scala 3 and allow comparing any types in Scala 2. This has the flaw that it's a regression in some cases for Scala 2 users and that `Eql[A, B]` is not really usable in its current form, see related discussion https://contributors.scala-lang.org/t/should-multiversal-equality-provide-default-eql-instances/4574 * Third attempt: implement "strict equality" for Scala 2 with a macro and `Eql[T, T]` in Scala. This improves the situation for Scala 2, but would mean relying on a feature that we can't easily port to Scala 3. * Fourth attempt (this commit): improve the first attempt (current release) by allowing `Compare[A, B]` as long as `A <:< B` OR `B <:< A`. This is possible thanks to an observation by Gabriele Petronella that it's possible to layer the implicits to avoid diverging implicit search. The benefit of the fourth approach is that it works the same way for Scala 3 and Scala 3. It's very nice that we can avoid macros as well.
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Previously, `Fixture[T]` was declared as an inner class of `FunSuite`. This made it annoying to implement fixtures as normal toplevel classes. Now, `Fixture[T]` is just a normal toplevel class making it easier to reason about. Breaking change: In order to implement this change, we remove the ability to extend `Suite` with a custom `type TestValue`. The test value is now hardcoded to `Future[Any]`. I'm not aware of any library that extends `munit.Suite` with a custom `TestValue`. All the 3rdparty integrations that I have seen hardcode against `munit.FunSuite` anyways. Given this feature doesn't seem to be used anywhere and it complicates the public API, I feel it's best to remove it.
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Superseded by #430 , which makes |
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Previously,
Fixture[T]was declared as an inner class ofFunSuite.This made it annoying to implement fixtures as normal toplevel classes.
Now,
Fixture[T]is just a normal toplevel class making it easier toreason about.
Breaking change: In order to implement this change, we remove the
ability to extend
Suitewith a customtype TestValue. The test valueis now hardcoded to
Future[Any]. I'm not aware of any library thatextends
munit.Suitewith a customTestValue. All the 3rdpartyintegrations that I have seen hardcode against
munit.FunSuiteanyways.Given this feature doesn't seem to be used anywhere and it complicates
the public API, I feel it's best to remove it.
Fixes #175
Waiting to merge #225 before moving further with this PR.