Squashed commits: scalafix-testkit3 cross compiled for scala3

This is the commit message scalacenter#2:

build sbt changes for test modules

This is the commit message scalacenter#3:

test modules: scalatest3V definition

build.sbt

@@ -173,7 +173,7 @@ lazy val testsShared = projectMatrix
     coverageEnabled := false
   )
   .defaultAxes(VirtualAxis.jvm)
-  .jvmPlatform(testTargetScalaVersions)
+  .jvmPlatform(buildScalaVersions :+ scala3)
   .disablePlugins(ScalafixPlugin)
 
 lazy val testsInput = projectMatrix
@@ -189,7 +189,7 @@ lazy val testsInput = projectMatrix
     coverageEnabled := false
   )
   .defaultAxes(VirtualAxis.jvm)
-  .jvmPlatform(testTargetScalaVersions)
+  .jvmPlatform(buildScalaVersions :+ scala3)
   .disablePlugins(ScalafixPlugin)
 
 lazy val testsOutput = projectMatrix
@@ -201,21 +201,24 @@ lazy val testsOutput = projectMatrix
     coverageEnabled := false
   )
   .defaultAxes(VirtualAxis.jvm)
-  .jvmPlatform(testTargetScalaVersions)
+  .jvmPlatform(buildScalaVersions :+ scala3)
   .disablePlugins(ScalafixPlugin)
 
 lazy val testkit = projectMatrix
   .in(file("scalafix-testkit"))
   .settings(
     moduleName := "scalafix-testkit",
     isFullCrossVersion,
-    libraryDependencies ++= Seq(
-      googleDiff,
-      scalatest
-    )
+    libraryDependencies += googleDiff,
+    libraryDependencies ++= {
+      if (!isScala3.value)
+        Seq(scalatest)
+      else
+        Seq("org.scalatest" %% "scalatest" % scalatest3V)
+    }
   )
   .defaultAxes(VirtualAxis.jvm)
-  .jvmPlatform(buildScalaVersions)
+  .jvmPlatform(buildScalaVersions :+ scala3)
   .dependsOn(cli)
 
 lazy val unit = projectMatrix

project/Dependencies.scala

@@ -35,6 +35,7 @@ object Dependencies {
   val scalaXml211V = "1.3.0" // scala-xml stops publishing for scala 2.11
   val scalametaV = "4.5.13"
   val scalatestV = "3.0.8" // don't bump, to avoid forcing breaking changes on clients via eviction
+  val scalatest3V = "3.2.13"
 
   val bijectionCore = "com.twitter" %% "bijection-core" % bijectionCoreV
   val collectionCompat = "org.scala-lang.modules" %% "scala-collection-compat" % collectionCompatV

project/ScalafixBuild.scala

@@ -146,7 +146,8 @@ object ScalafixBuild extends AutoPlugin with GhpagesKeys {
         "core3/compile" ::
         "rules3/compile" ::
         "reflect3/compile" ::
-        "cli3/compile" :: // TODO replace core rules and reflect with unit3 in the end
+        "cli3/compile" ::
+        "testkit3/compile" :: // TODO replace core rules and reflect with unit3 in the end
         s
     },
     commands += Command.command("ci-213") { s =>

scalafix-testkit/src/main/scala/scalafix/testkit/SemanticRuleSuite.scala

@@ -1,6 +1,7 @@
 package scalafix.testkit
 
 import scala.meta._
+import scala.meta.internal.inputs.XtensionInputSyntaxStructure
 
 import scalafix.internal.reflect.RuleCompilerClasspath
 import scalafix.internal.testkit.EndOfLineAssertExtractor