task done (Kozyrev Egor)

src/test/java/option/OptionalExample.java

@@ -5,6 +5,7 @@
 import java.util.Optional;
 import java.util.concurrent.ThreadLocalRandom;
 import java.util.function.Function;
+import java.util.function.Predicate;
 
 import static org.junit.Assert.assertEquals;
 
@@ -50,9 +51,61 @@ public void map() {
         assertEquals(expected, actual);
     }
 
+    @Test
+    public void testFilter() {
+        final Optional<String> o1 = getOptional();
+
+        final Predicate<String> p = String::isEmpty;
+
+        final Optional<String> expected = o1.filter(p);
+
+        final Optional<String> actual;
+        if (o1.isPresent() && p.test(o1.get())) {
+            actual = Optional.of(o1.get());
+        } else {
+            actual = Optional.empty();
+        }
+
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    public void testOrElse() {
+        final Optional<String> o1 = getOptional();
+
+        final String expected = o1.orElse("else");
+
+        final String actual;
+        if (o1.isPresent()) {
+            actual = o1.get();
+        } else {
+            actual = "else";
+        }
+
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    public void testFlatMap() {
+        final Optional<String> o1 = getOptional();
+
+        final Function<String, Optional<String>> function = Optional::of;
+
+        final Optional<String> expected = o1.flatMap(function);
+
+        final Optional<String> actual;
+        if (o1.isPresent()) {
+            actual = function.apply(o1.get());
+        } else {
+            actual = Optional.empty();
+        }
+
+        assertEquals(expected, actual);
+    }
+
     private Optional<String> getOptional() {
         return ThreadLocalRandom.current().nextBoolean()
-            ? Optional.empty()
-            : Optional.of("abc");
+                ? Optional.empty()
+                : Optional.of("abc");
     }
 }