scalafix-testkit users cannot use scalatest >= 3.2.0

[bjaglin]

See #1083

Experienced in scalacenter/sbt-scalafix#131: scalatest 3.1.x users could still use scalafix-testkit as long as they didn't treat deprecations as warnings, but scalatest 3.2.x cannot as deprecated classes have been removed.

[bjaglin]

Maybe we could publish several scalafix-testkit versions, one for each breaking change of scalatest?

[olafurpg]

Is there a stable ScalaTest API that we could use that's consistent between 3.0 and 3.1? Scalafix testkit doesn't need much from ScalaTest, just the ability to submit a test with a name and body.

I have considered replacing the ScalaTest dependency in favor of MUnit/JUnit for Scalafix 1.x. The binary breaking changes in ScalaTest 3.1.x make it hard to support a library API such as scalafix-testkit.

At Twitter, we have many custom Scalafix rules that are tested with scalafix-testkit and we're still on ScalaTest 3.0.x and I don't know when we will invest in doing the 3.1.x upgrade. It might happen soon, it might happen next year.

Cross-building testkit against two ScalaTest versions is the path of resistance. We could publish the 3.2.x artifacts with an additional _scalatest3.2 suffix and keep the current 3.0.x artifact unchanged (no suffix).

[bjaglin]

Is there a stable ScalaTest API that we could use that's consistent between 3.0 and 3.1?

Good point, I'll have a look.

I don't know when we will invest in doing the 3.1.x upgrade

Out of curiosity, why isnt' https://github.com/scalatest/autofix/tree/master/3.1.x enough for a smooth migration? Other libraries built against scalatest like scalafix maybe?

We could publish the 3.2.x artifacts with an additional _scalatest3.2 suffix and keep the current 3.0.x artifact unchanged (no suffix).

That's what I had in mind, but I agree that should be the last resort.