Port tests for InjectK to new tests for Inject

Author: andyscott

core/src/main/scala/cats/Inject.scala

@@ -3,17 +3,17 @@ package cats
 /**
  * Inject is a type class to inject a value of type `A` into a
  * coproduct of types `B` when `A :≺: B`. The coproduct `B` is
- * modelled with [[Either]].
+ * modelled with [[scala.util.Either]].
  *
  * The injection type is described thoroughly in "Data types a la
  * carte" (Swierstra 2008).
  *
  * @since 1.0
  * @note Prior to cats 1.0, Inject handled injection for type
- * constructors.  For injection of type constructors, use [[InjectK]].
+ * constructors. For injection of type constructors into [[data.EitherK]],
+ * use [[InjectK]].
  *
  * @see [[http://www.staff.science.uu.nl/~swier004/publications/2008-jfp.pdf]]
- * @see [[InjectK]] for injection for [[EitherK]]
  */
 sealed abstract class Inject[A, B] {
   def inj: A => B

core/src/main/scala/cats/InjectK.scala

@@ -14,7 +14,7 @@ import cats.data.EitherK
  * @note Prior to cats 1.0, InjectK was known as [[Inject]].
  *
  * @see [[http://www.staff.science.uu.nl/~swier004/publications/2008-jfp.pdf]]
- * @see [[Inject]] for injection for [[Either]]
+ * @see [[Inject]] for injection for [[scala.util.Either]].
  */
 sealed abstract class InjectK[F[_], G[_]] {
   def inj: FunctionK[F, G]

tests/src/test/scala/cats/tests/InjectTests.scala

@@ -0,0 +1,65 @@
+package cats
+
+import cats.tests.CatsSuite
+
+class InjectTests extends CatsSuite {
+
+  type StringOrInt = Either[String, Int]
+
+  test("inj & prj") {
+    def distr[F](f1: F, f2: F)
+      (implicit
+        I0: Inject[String, F],
+        I1: Inject[Int, F]
+      ): Option[String] =
+      for {
+        x <- I0.prj(f1)
+        y <- I1.prj(f2)
+      } yield s"$x $y"
+
+    forAll { (x: String, y: Int) =>
+      val expr1: StringOrInt = Inject[String, StringOrInt].inj(x)
+      val expr2: StringOrInt = Inject[Int, StringOrInt].inj(y)
+      val res = distr(expr1, expr2)
+      res should ===(Some(s"$x $y"))
+    }
+  }
+
+  test("apply & unapply") {
+    def distr[F](f1: F, f2: F)
+      (implicit
+        I0: Inject[String, F],
+        I1: Inject[Int, F]
+      ): Option[String] =
+      for {
+        x <- I0.unapply(f1)
+        y <- I1.unapply(f2)
+      } yield s"$x $y"
+
+    forAll { (x: String, y: Int) =>
+      val expr1: StringOrInt = Inject[String, StringOrInt].apply(x)
+      val expr2: StringOrInt = Inject[Int, StringOrInt].apply(y)
+      val res = distr(expr1, expr2)
+      res should ===(Some(s"$x $y"))
+    }
+  }
+
+  test("apply in left") {
+    forAll { (y: String) =>
+      Inject[String, StringOrInt].inj(y) == Left(y) should ===(true)
+    }
+  }
+
+  test("apply in right") {
+    forAll { (y: Int) =>
+      Inject[Int, StringOrInt].inj(y) == Right(y) should ===(true)
+    }
+  }
+
+  test("null identity") {
+    val stringNull = null.asInstanceOf[String]
+    Inject.catsReflexiveInjectInstance[String].inj(stringNull) should ===(stringNull)
+    Inject.catsReflexiveInjectInstance[String].prj(stringNull) should ===(Some(stringNull))
+  }
+
+}