Add Validated.swap

core/src/main/scala/cats/data/Validated.scala

@@ -189,6 +189,10 @@ sealed abstract class Validated[+E, +A] extends Product with Serializable {
       case _ => that
     }
 
+  def swap: Validated[A, E] = this match {
+    case Valid(a) => Invalid(a)
+    case Invalid(e) => Valid(e)
+  }
 }
 
 object Validated extends ValidatedInstances with ValidatedFunctions{

tests/src/test/scala/cats/tests/CoproductTests.scala

@@ -51,4 +51,17 @@ class CoproductTests extends CatsSuite {
     }
   }
 
+  test("swap negates isLeft/isRight") {
+    forAll { (x: Coproduct[Option, Option, Int]) =>
+      x.isLeft should !== (x.swap.isLeft)
+      x.isRight should !== (x.swap.isRight)
+    }
+  }
+
+  test("isLeft consistent with isRight") {
+    forAll { (x: Coproduct[Option, Option, Int]) =>
+      x.isLeft should !== (x.isRight)
+    }
+  }
+
 }

tests/src/test/scala/cats/tests/ValidatedTests.scala

@@ -154,4 +154,23 @@ class ValidatedTests extends CatsSuite {
     }
   }
 
+  test("isInvalid consistent with isValid") {
+    forAll { (x: Validated[String, Int]) =>
+      x.isInvalid should !== (x.isValid)
+    }
+  }
+
+  test("double swap is identity") {
+    forAll { (x: Validated[String, Int]) =>
+      x.swap.swap should ===(x)
+    }
+  }
+
+  test("swap negates isInvalid/isValid") {
+    forAll { (x: Validated[String, Int]) =>
+      x.isInvalid should !== (x.swap.isInvalid)
+      x.isValid should !== (x.swap.isValid)
+    }
+  }
+
 }

tests/src/test/scala/cats/tests/XorTests.scala

@@ -89,6 +89,19 @@ class XorTests extends CatsSuite {
     }
   }
 
+  test("swap negates isLeft/isRight") {
+    forAll { (x: Int Xor String) =>
+      x.isLeft should !== (x.swap.isLeft)
+      x.isRight should !== (x.swap.isRight)
+    }
+  }
+
+  test("isLeft consistent with isRight") {
+    forAll { (x: Int Xor String) =>
+      x.isLeft should !== (x.isRight)
+    }
+  }
+
   test("foreach is noop for left") {
     forAll { (x: Int Xor String) =>
       var count = 0