diff --git a/.scalafmt.conf b/.scalafmt.conf
index d45701aa..b4486c93 100644
--- a/.scalafmt.conf
+++ b/.scalafmt.conf
@@ -1,4 +1,5 @@
-version = "2.7.5"
+version = "3.0.0"
+runner.dialect = "scala3"
 align.preset = none
 maxColumn = 120
 includeNoParensInSelectChains = false
diff --git a/core/src/test/scala-3/cats/derived/FoldableSuite.scala b/core/src/test/scala-3/cats/derived/FoldableSuite.scala
new file mode 100644
index 00000000..ff03f9af
--- /dev/null
+++ b/core/src/test/scala-3/cats/derived/FoldableSuite.scala
@@ -0,0 +1,102 @@
+/*
+ * Copyright (c) 2015 Miles Sabin
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package cats
+package derived
+
+import cats.laws.discipline.{FoldableTests, SerializableTests}
+import cats.syntax.all.*
+import org.scalacheck.Arbitrary
+import scala.compiletime.*
+
+class FoldableSuite extends KittensSuite:
+  import FoldableSuite.*
+  import TestDefns.*
+
+  inline def foldableTests[F[_]]: FoldableTests[F] =
+    FoldableTests[F](summonInline)
+
+  inline def testFoldable(inline context: String): Unit =
+    checkAll(s"$context.Foldable[IList]", foldableTests[IList].foldable[Int, Long])
+    checkAll(s"$context.Foldable[Tree]", foldableTests[Tree].foldable[Int, Long])
+    checkAll(s"$context.Foldable[GenericAdt]", foldableTests[GenericAdt].foldable[Int, Long])
+    checkAll(s"$context.Foldable[OptList]", foldableTests[OptList].foldable[Int, Long])
+    checkAll(s"$context.Foldable[ListSnoc]", foldableTests[ListSnoc].foldable[Int, Long])
+    checkAll(s"$context.Foldable[AndChar]", foldableTests[AndChar].foldable[Int, Long])
+    checkAll(s"$context.Foldable[Interleaved]", foldableTests[Interleaved].foldable[Int, Long])
+    checkAll(s"$context.Foldable[BoxNel]", foldableTests[BoxNel].foldable[Int, Long])
+    checkAll(s"$context.Foldable is Serializable", SerializableTests.serializable(summonInline[Foldable[Tree]]))
+
+  locally {
+    import auto.foldable.given
+    testFoldable("auto")
+  }
+
+  locally {
+    import semiInstances.given
+    testFoldable("semiauto")
+  }
+
+end FoldableSuite
+
+object FoldableSuite:
+  import TestDefns.*
+
+  type OptList[A] = Option[List[A]]
+  type ListSnoc[A] = List[Snoc[A]]
+  type AndChar[A] = (A, Char)
+  type BoxNel[A] = Box[Nel[A]]
+
+  object semiInstances:
+    given Foldable[IList] = semiauto.foldable
+    given Foldable[Tree] = semiauto.foldable
+    given Foldable[GenericAdt] = semiauto.foldable
+    given Foldable[OptList] = semiauto.foldable
+    given Foldable[ListSnoc] = semiauto.foldable
+    given Foldable[AndChar] = semiauto.foldable
+    given Foldable[Interleaved] = semiauto.foldable
+    given Foldable[BoxNel] = semiauto.foldable
+
+  final case class Nel[+A](head: A, tail: List[A])
+  object Nel:
+    given [A: Eq]: Eq[Nel[A]] =
+      (x, y) => x.head === y.head && x.tail === y.tail
+
+    given [A: Arbitrary]: Arbitrary[Nel[A]] =
+      Arbitrary(for
+        head <- Arbitrary.arbitrary[A]
+        tail <- Arbitrary.arbitrary[List[A]]
+      yield Nel(head, tail))
+
+    given Foldable[Nel] with
+      def foldLeft[A, B](fa: Nel[A], b: B)(f: (B, A) => B) = fa.tail.foldl(b)(f)
+      def foldRight[A, B](fa: Nel[A], lb: Eval[B])(f: (A, Eval[B]) => Eval[B]) = fa.tail.foldr(lb)(f)
+
+  case class Single[A](value: A) derives Foldable
+
+  enum Many[+A] derives Foldable:
+    case Naught
+    case More(value: A, rest: Many[A])
+
+  enum AtMostOne[+A] derives Foldable:
+    case Naught
+    case Single(value: A)
+
+  enum AtLeastOne[+A] derives Foldable:
+    case Single(value: A)
+    case More(value: A, rest: Option[AtLeastOne[A]])
+
+end FoldableSuite
diff --git a/core/src/test/scala-3/cats/derived/FoldableTests.scala b/core/src/test/scala-3/cats/derived/FoldableTests.scala
deleted file mode 100644
index 4bb39f00..00000000
--- a/core/src/test/scala-3/cats/derived/FoldableTests.scala
+++ /dev/null
@@ -1,17 +0,0 @@
-package cats.derived
-
-import cats.Foldable
-import cats.derived.*
-
-class FoldableTests {
-
-  case class Box[A](value: A) derives Foldable
-
-  sealed trait Maybe[+A] derives Foldable
-  case object Nufin extends Maybe[Nothing]
-  case class Just[A](value: A) extends Maybe[A]
-
-  sealed trait CList[A] derives Foldable
-  case object CNil extends CList[Nothing]
-  case class CCons[A](head: A, tail: CList[A]) extends CList[A]
-}
diff --git a/core/src/test/scala-3/cats/derived/FunctorSuite.scala b/core/src/test/scala-3/cats/derived/FunctorSuite.scala
new file mode 100644
index 00000000..80d9445e
--- /dev/null
+++ b/core/src/test/scala-3/cats/derived/FunctorSuite.scala
@@ -0,0 +1,91 @@
+/*
+ * Copyright (c) 2015 Miles Sabin
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package cats
+package derived
+
+import cats.laws.discipline.*
+import cats.laws.discipline.eq.*
+import scala.compiletime.*
+
+class FunctorSuite extends KittensSuite:
+  import FunctorSuite.*
+  import TestDefns.*
+
+  given ExhaustiveCheck[Predicate[Boolean]] =
+    ExhaustiveCheck.instance(List(_ => true, _ => false, identity, !_))
+
+  inline def functorTests[F[_]]: FunctorTests[F] =
+    FunctorTests[F](summonInline)
+
+  inline def testFunctor(inline context: String): Unit =
+    checkAll(s"$context.Functor[IList]", functorTests[IList].functor[Int, String, Long])
+    checkAll(s"$context.Functor[Tree]", functorTests[Tree].functor[Int, String, Long])
+    checkAll(s"$context.Functor[GenericAdt]", functorTests[GenericAdt].functor[Int, String, Long])
+    checkAll(s"$context.Functor[OptList]", functorTests[OptList].functor[Int, String, Long])
+    checkAll(s"$context.Functor[ListSnoc]", functorTests[ListSnoc].functor[Int, String, Long])
+    // FIXME: Testing `functorTests[AndChar].functor[Int, String, Long]` causes a ClassCastException
+    checkAll(s"$context.Functor[AndChar]", functorTests[AndChar].functor[Int, String, Int])
+    checkAll(s"$context.Functor[Interleaved]", functorTests[Interleaved].functor[Int, String, Long])
+    checkAll(s"$context.Functor[NestedPred]", functorTests[NestedPred].functor[Boolean, Int, Boolean])
+    checkAll(s"$context.Functor is Serializable", SerializableTests.serializable(summonInline[Functor[Tree]]))
+
+  locally {
+    import auto.functor.given
+    testFunctor("auto")
+  }
+
+  locally {
+    import semiInstances.given
+    testFunctor("semiauto")
+  }
+
+end FunctorSuite
+
+object FunctorSuite:
+  import TestDefns.*
+
+  type OptList[A] = Option[List[A]]
+  type ListSnoc[A] = List[Snoc[A]]
+  type AndChar[A] = (A, Char)
+  type Predicate[A] = A => Boolean
+  type NestedPred[A] = Predicate[Predicate[A]]
+
+  object semiInstances:
+    given Functor[IList] = semiauto.functor
+    given Functor[Tree] = semiauto.functor
+    given Functor[GenericAdt] = semiauto.functor
+    given Functor[OptList] = semiauto.functor
+    given Functor[ListSnoc] = semiauto.functor
+    given Functor[AndChar] = semiauto.functor
+    given Functor[Interleaved] = semiauto.functor
+    given Functor[NestedPred] = semiauto.functor
+
+  case class Single[A](value: A) derives Functor
+
+  enum Many[+A] derives Functor:
+    case Naught
+    case More(value: A, rest: Many[A])
+
+  enum AtMostOne[+A] derives Functor:
+    case Naught
+    case Single(value: A)
+
+  enum AtLeastOne[+A] derives Functor:
+    case Single(value: A)
+    case More(value: A, rest: Option[AtLeastOne[A]])
+
+end FunctorSuite
diff --git a/core/src/test/scala-3/cats/derived/FunctorTests.scala b/core/src/test/scala-3/cats/derived/FunctorTests.scala
deleted file mode 100644
index d97ff399..00000000
--- a/core/src/test/scala-3/cats/derived/FunctorTests.scala
+++ /dev/null
@@ -1,18 +0,0 @@
-package cats.derived
-
-import cats.Functor
-import cats.derived.*
-
-class FunctorTests {
-
-  case class Box[A](value: A) derives Functor
-
-  sealed trait Maybe[+A] derives Functor
-  case object Nufin extends Maybe[Nothing]
-  case class Just[A](value: A) extends Maybe[A]
-
-  sealed trait CList[A] derives Functor
-  case object CNil extends CList[Nothing]
-  case class CCons[A](head: A, tail: CList[A]) extends CList[A]
-
-}
diff --git a/core/src/test/scala-3/cats/derived/functor.scala b/core/src/test/scala-3/cats/derived/functor.scala
deleted file mode 100644
index 96ca253b..00000000
--- a/core/src/test/scala-3/cats/derived/functor.scala
+++ /dev/null
@@ -1,77 +0,0 @@
-/*
- * Copyright (c) 2015 Miles Sabin
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-package cats
-package derived
-
-import cats.laws.discipline._
-import cats.laws.discipline.eq._
-
-class FunctorSuite extends KittensSuite {
-  import TestDefns.*
-
-  implicit val exhaustivePred: ExhaustiveCheck[Predicate[Boolean]] =
-    ExhaustiveCheck.instance(List(_ => true, _ => false, identity, !_))
-
-  def testFunctor(context: String)(implicit
-      iList: Functor[IList],
-      tree: Functor[Tree],
-      genericAdt: Functor[GenericAdt],
-      optList: Functor[OptList],
-      listSnoc: Functor[ListSnoc],
-      andChar: Functor[AndChar],
-      interleaved: Functor[Interleaved],
-      nestedPred: Functor[NestedPred]
-  ): Unit = {
-    checkAll(s"$context.Functor[IList]", FunctorTests[IList].functor[Int, String, Long])
-    checkAll(s"$context.Functor[Tree]", FunctorTests[Tree].functor[Int, String, Long])
-    checkAll(s"$context.Functor[GenericAdt]", FunctorTests[GenericAdt].functor[Int, String, Long])
-    checkAll(s"$context.Functor[OptList]", FunctorTests[OptList].functor[Int, String, Long])
-    checkAll(s"$context.Functor[ListSnoc]", FunctorTests[ListSnoc].functor[Int, String, Long])
-    // FIXME: Testing `FunctorTests[AndChar].functor[Int, String, Int]` causes a ClassCastException
-    checkAll(s"$context.Functor[AndChar]", FunctorTests[AndChar].functor[Int, String, Int])
-    checkAll(s"$context.Functor[Interleaved]", FunctorTests[Interleaved].functor[Int, String, Long])
-    checkAll(s"$context.Functor[NestedPred]", FunctorTests[NestedPred].functor[Boolean, Int, Boolean])
-    checkAll(s"$context.Functor is Serializable", SerializableTests.serializable(Functor[Tree]))
-  }
-
-  {
-    import auto.functor.given
-    testFunctor("auto")
-  }
-
-  {
-    import semiInstances._
-    testFunctor("semiauto")
-  }
-
-  type OptList[A] = Option[List[A]]
-  type ListSnoc[A] = List[Snoc[A]]
-  type AndChar[A] = (A, Char)
-  type Predicate[A] = A => Boolean
-  type NestedPred[A] = Predicate[Predicate[A]]
-
-  object semiInstances {
-    implicit val iList: Functor[IList] = semiauto.functor
-    implicit val tree: Functor[Tree] = semiauto.functor
-    implicit val genericAdt: Functor[GenericAdt] = semiauto.functor
-    implicit val optList: Functor[OptList] = semiauto.functor
-    implicit val listSnoc: Functor[ListSnoc] = semiauto.functor
-    implicit val andChar: Functor[AndChar] = semiauto.functor
-    implicit val interleaved: Functor[Interleaved] = semiauto.functor
-    implicit val nestedPred: Functor[NestedPred] = semiauto.functor
-  }
-}