[BAEL-5211] - How to test a Java Optional (#11417)

* feat: add how to test an optional

* fix: review comments

* fix: static final naming convention

* fix: optional equals assertion

testing-modules/testing-assertions/src/test/java/com/baeldung/optional/OptionalUnitTest.java

@@ -0,0 +1,58 @@
+package com.baeldung.optional;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.Optional;
+
+import static org.assertj.core.api.AssertionsForClassTypes.assertThat;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+class OptionalUnitTest {
+
+    private static final String OPTIONAL_RETURN_VALUE = "optionalReturnValue";
+
+    @Test
+    public void givenOptionalWithValue_whenAssertThatIsNotEmpty_thenOk() {
+        assertThat(Optional.of(OPTIONAL_RETURN_VALUE)).isNotEmpty();
+    }
+
+    @Test
+    public void givenOptionalWithValue_whenAssertThatHasValue_thenOk() {
+        assertThat(Optional.of(OPTIONAL_RETURN_VALUE)).hasValue(OPTIONAL_RETURN_VALUE);
+    }
+
+    @Test
+    public void givenOptionalWithValue_whenAssertEqualsOptionalObject_thenOk() {
+        Optional<String> expected = Optional.of(OPTIONAL_RETURN_VALUE);
+        Optional<String> actual = Optional.of(OPTIONAL_RETURN_VALUE);
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    public void givenOptionalWithValue_whenAssertEqualsGet_thenOk() {
+        Optional<String> optional = Optional.of(OPTIONAL_RETURN_VALUE);
+        assertEquals(OPTIONAL_RETURN_VALUE, optional.get());
+    }
+
+    @Test
+    public void givenOptionalWithValue_whenIsPresentAndGetSplit_thenOk() {
+        Optional<String> optional = Optional.of(OPTIONAL_RETURN_VALUE);
+
+        assertTrue(optional.isPresent());
+        assertEquals(OPTIONAL_RETURN_VALUE, optional.get());
+    }
+
+    @Test
+    public void givenEmptyOptional_whenAssertThatIsEmpty_thenOk() {
+        Optional<String> emptyOptional = Optional.empty();
+        assertThat(emptyOptional).isEmpty();
+    }
+
+    @Test
+    public void givenEmptyOptional_whenAssertIsNotPresent_thenOk() {
+        Optional<String> emptyOptional = Optional.empty();
+        assertFalse(emptyOptional.isPresent());
+    }
+}