Added isRight assertion

Author: rcardin-lm

src/main/kotlin/in/rcard/assertj/arrowcore/AbstractEitherAssert.kt

@@ -4,4 +4,11 @@ import arrow.core.Either
 import org.assertj.core.api.AbstractObjectAssert
 
 abstract class AbstractEitherAssert<SELF : AbstractEitherAssert<SELF, LEFT, RIGHT>, LEFT, RIGHT>(either: Either<LEFT, RIGHT>?) :
-    AbstractObjectAssert<SELF, Either<LEFT, RIGHT>>(either, AbstractEitherAssert::class.java)
+    AbstractObjectAssert<SELF, Either<LEFT, RIGHT>>(either, AbstractEitherAssert::class.java) {
+    fun isRight() {
+        isNotNull
+        if (!actual.isRight()) {
+            failWithMessage("%nExpected Either to be right but was <%s>", actual)
+        }
+    }
+}

src/test/kotlin/in/rcard/assertj/arrowcore/EitherAssert_isRight_Test.kt

@@ -0,0 +1,39 @@
+package `in`.rcard.assertj.arrowcore
+
+import arrow.core.Either
+import arrow.core.left
+import arrow.core.right
+import org.assertj.core.api.Assertions
+import org.assertj.core.util.FailureMessages.actualIsNull
+import org.junit.jupiter.api.Test
+
+class EitherAssert_isRight_Test {
+
+    @Test
+    fun `should fail if either is null`() {
+        // GIVEN
+        val rightValue: Either<Nothing, Nothing>? = null
+        // WHEN/THEN
+        Assertions.assertThatThrownBy { EitherAssert.assertThat(rightValue).isRight() }
+            .isInstanceOf(AssertionError::class.java)
+            .hasMessage(actualIsNull())
+    }
+
+    @Test
+    fun `should pass if either is right`() {
+        // GIVEN
+        val rightValue = 42.right()
+        // WHEN/THEN
+        EitherAssert.assertThat(rightValue).isRight()
+    }
+
+    @Test
+    fun `should fail if either is left`() {
+        // GIVEN
+        val leftValue = "42".left()
+        // WHEN/THEN
+        Assertions.assertThatThrownBy { EitherAssert.assertThat(leftValue).isRight() }
+            .isInstanceOf(AssertionError::class.java)
+            .hasMessage("\nExpected Either to be right but was <Either.Left(42)>")
+    }
+}