Add blocking and non-blocking mono examples

Add article reference

Fix url

reactor-core/README.md

@@ -7,3 +7,4 @@ This module contains articles about Reactor Core.
 - [Intro To Reactor Core](https://www.baeldung.com/reactor-core)
 - [Combining Publishers in Project Reactor](https://www.baeldung.com/reactor-combine-streams)
 - [Programmatically Creating Sequences with Project Reactor](https://www.baeldung.com/flux-sequences-reactor)
+- [How To Get String From Mono In Reactive Java](http://baeldung.com/string-from-mono/)

reactor-core/src/test/java/com/baeldung/mono/MonoUnitTest.java

@@ -0,0 +1,39 @@
+package com.baeldung.mono;
+
+import org.junit.Test;
+import reactor.core.publisher.Mono;
+
+import java.time.Duration;
+import java.time.temporal.ChronoUnit;
+import java.util.Optional;
+
+import static org.junit.Assert.assertEquals;
+
+public class MonoUnitTest {
+    @Test
+    public void whenMonoProducesString_thenBlockAndConsume() {
+        String expected = "hello world!";
+
+        String result1 = Mono.just(expected).block();
+        assertEquals(expected, result1);
+
+        String result2 = Mono.just(expected).block(Duration.of(1000, ChronoUnit.MILLIS));
+        assertEquals(expected, result2);
+
+        Optional<String> result3 = Mono.<String>empty().blockOptional();
+        assertEquals(Optional.empty(), result3);
+    }
+
+    @Test
+    public void whenMonoProducesString_thenConsumeNonBlocking() {
+        String expected = "hello world!";
+
+        Mono.just(expected)
+                .doOnNext(result -> assertEquals(expected, result))
+                .subscribe();
+
+        Mono.just(expected)
+                .subscribe(result -> assertEquals(expected, result));
+
+    }
+}