retry when rxjava (#12961)

* BAEL-5751 test commit for checkin builds

* BAEL-5751 compiled with java 8

* BAEL-5751 small update

* BAEL-5751 added the core code

* BAEL-5751 moved code to a different module

* BAEL-5751 using assertArrayEquals

* BAEL-5751 new line at the end of file

* BAEL-5738 retry with delay in rxJava

* Update RxJavaRetryWithDelayUnitTest.java

Co-authored-by: Grzegorz Piwowarek <gpiwowarek@gmail.com>

rxjava-modules/rxjava-core/src/test/java/com/baeldung/rxjava/RxJavaRetryWithDelayUnitTest.java

@@ -0,0 +1,62 @@
+package com.baeldung.rxjava;
+import io.reactivex.Observable;
+import org.junit.Test;
+
+import java.util.concurrent.TimeUnit;
+
+public class RxJavaRetryWithDelayUnitTest {
+
+    @Test
+    public void givenObservable_whenSuccess_thenOnNext(){
+        Observable.just(remoteCallSuccess())
+                .subscribe(success -> {
+                    System.out.println("Success");
+                    System.out.println(success);
+                }, err -> {
+                    System.out.println("Error");
+                    System.out.println(err);
+                });
+    }
+
+
+    @Test
+    public void givenObservable_whenError_thenOnError(){
+        Observable.just(remoteCallError())
+                .subscribe(success -> {
+                    System.out.println("Success");
+                    System.out.println(success);
+                }, err -> {
+                    System.out.println("Error");
+                    System.out.println(err);
+                });
+    }
+
+    @Test
+    public void givenError_whenRetry_thenCanDelay(){
+        Observable.just(remoteCallError())
+                .retryWhen(attempts -> {
+                    return attempts.flatMap(err -> {
+                        if (customChecker(err)) {
+                            return Observable.timer(5000, TimeUnit.MILLISECONDS);
+                        } else {
+                            return Observable.error(err);
+                        }
+                    });
+                });
+    }
+
+
+    private String remoteCallSuccess(){
+        return "Success";
+    }
+
+    private String remoteCallError(){
+        // consider a network call that failed over here.
+        return "Error";
+    }
+
+    private boolean customChecker(Throwable t){
+        // this will include custom logic that decides whether resubscription should occur or not
+        return true;
+    }
+}