Added the isDefined assertion

Author: rcardin

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

@@ -1,6 +1,7 @@
 package `in`.rcard.assertj.arrowcore
 
 import arrow.core.Option
+import `in`.rcard.assertj.arrowcore.errors.OptionShouldBePresent.Companion.shouldBePresent
 import org.assertj.core.api.AbstractObjectAssert
 
 /**
@@ -14,4 +15,16 @@ abstract class AbstractOptionAssert<
     SELF : AbstractOptionAssert<SELF, VALUE>, VALUE : Any,
     >(
     option: Option<VALUE>?,
-) : AbstractObjectAssert<SELF, Option<VALUE>>(option, AbstractOptionAssert::class.java)
+) : AbstractObjectAssert<SELF, Option<VALUE>>(option, AbstractOptionAssert::class.java) {
+
+    /**
+     * Verifies that there is a value present in the actual [Option].
+     *
+     * @return this assertion object.
+     */
+    fun isDefined(): SELF {
+        isNotNull
+        if (actual.isEmpty()) throwAssertionError(shouldBePresent())
+        return myself
+    }
+}

src/main/kotlin/in/rcard/assertj/arrowcore/errors/OptionShouldBePresent.kt

@@ -0,0 +1,24 @@
+package `in`.rcard.assertj.arrowcore.errors
+
+import arrow.core.Option
+import org.assertj.core.error.BasicErrorMessageFactory
+
+/**
+ * Build error message when a value should be present in an [Option].
+ *
+ * @author Riccardo Cardin
+ */
+class OptionShouldBePresent :
+    BasicErrorMessageFactory("%nExpecting Option to contain a value but it didn't.".format()) {
+    companion object {
+
+        /**
+         * Indicates that a value should be present in an empty [Option].
+         *
+         * @return a error message factory.
+         */
+        fun shouldBePresent(): OptionShouldBePresent {
+            return OptionShouldBePresent()
+        }
+    }
+}

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

@@ -0,0 +1,32 @@
+package `in`.rcard.assertj.arrowcore
+
+import arrow.core.None
+import arrow.core.Option
+import arrow.core.some
+import `in`.rcard.assertj.arrowcore.OptionAssert.Companion.assertThat
+import `in`.rcard.assertj.arrowcore.errors.OptionShouldBePresent.Companion.shouldBePresent
+import org.assertj.core.api.Assertions
+import org.assertj.core.util.FailureMessages.actualIsNull
+import org.junit.jupiter.api.Test
+
+class OptionAssert_isDefined_Test {
+    @Test
+    fun `should pass when Option is present`() {
+        assertThat("present".some()).isDefined()
+    }
+
+    @Test
+    fun `should fail when Option is empty`() {
+        Assertions.assertThatThrownBy { assertThat(None).isDefined() }
+            .isInstanceOf(AssertionError::class.java)
+            .hasMessage(shouldBePresent().create())
+    }
+
+    @Test
+    fun `should fail when Option is null`() {
+        val nullOption: Option<Nothing>? = null
+        Assertions.assertThatThrownBy { assertThat(nullOption).isDefined() }
+            .isInstanceOf(AssertionError::class.java)
+            .hasMessage(actualIsNull())
+    }
+}