testing with StepVerifier (#5673)

* testing with StepVerifier

* Test publisher

spring-5-reactive/pom.xml

@@ -143,7 +143,7 @@
         <jsonb-api.version>1.0</jsonb-api.version>
         <geronimo-json_1.1_spec.version>1.0</geronimo-json_1.1_spec.version>
         <commons-collections4.version>4.1</commons-collections4.version>
-        <project-reactor-test>3.1.6.RELEASE</project-reactor-test>
+        <project-reactor-test>3.2.3.RELEASE</project-reactor-test>
     </properties>
 
 </project>

spring-5-reactive/src/test/java/com/baeldung/stepverifier/PostExecutionUnitTest.java

@@ -0,0 +1,34 @@
+package com.baeldung.stepverifier;
+
+import org.junit.Test;
+import reactor.core.publisher.Flux;
+import reactor.test.StepVerifier;
+
+import java.time.Duration;
+
+public class PostExecutionUnitTest {
+
+    Flux<Integer> source = Flux.<Integer>create(emitter -> {
+        emitter.next(1);
+        emitter.next(2);
+        emitter.next(3);
+        emitter.complete();
+        try {
+            Thread.sleep(1000);
+        } catch (InterruptedException e) {
+            e.printStackTrace();
+        }
+        emitter.next(4);
+    }).filter(number -> number % 2 == 0);
+
+    @Test
+    public void droppedElements() {
+        StepVerifier.create(source)
+          .expectNext(2)
+          .expectComplete()
+          .verifyThenAssertThat()
+          .hasDropped(4)
+          .tookLessThan(Duration.ofMillis(1050));
+    }
+
+}

spring-5-reactive/src/test/java/com/baeldung/stepverifier/StepByStepUnitTest.java

@@ -0,0 +1,39 @@
+package com.baeldung.stepverifier;
+
+import org.junit.Test;
+import reactor.core.publisher.Flux;
+import reactor.core.publisher.Mono;
+import reactor.test.StepVerifier;
+
+public class StepByStepUnitTest {
+
+    Flux<String> source = Flux.just("John", "Monica", "Mark", "Cloe", "Frank", "Casper", "Olivia", "Emily", "Cate")
+      .filter(name -> name.length() == 4)
+      .map(String::toUpperCase);
+
+    @Test
+    public void shouldReturnForLettersUpperCaseStrings() {
+        StepVerifier
+          .create(source)
+          .expectNext("JOHN")
+          .expectNextMatches(name -> name.startsWith("MA"))
+          .expectNext("CLOE", "CATE")
+          .expectComplete()
+          .verify();
+    }
+
+    @Test
+    public void shouldThrowExceptionAfterFourElements() {
+        Flux<String> error = source.concatWith(
+          Mono.error(new IllegalArgumentException("Our message"))
+        );
+
+        StepVerifier
+          .create(error)
+          .expectNextCount(4)
+          .expectErrorMatches(throwable -> throwable instanceof IllegalArgumentException &&
+                  throwable.getMessage().equals("Our message")
+          ).verify();
+    }
+
+}

spring-5-reactive/src/test/java/com/baeldung/stepverifier/TestingTestPublisherUnitTest.java

@@ -0,0 +1,51 @@
+package com.baeldung.stepverifier;
+
+import org.junit.Test;
+import reactor.core.publisher.Flux;
+import reactor.test.StepVerifier;
+import reactor.test.publisher.TestPublisher;
+
+public class TestingTestPublisherUnitTest {
+
+    @Test
+    public void testPublisher() {
+        TestPublisher
+          .<String>create()
+          .next("First", "Second", "Third")
+          .error(new RuntimeException("Message"));
+    }
+
+    @Test
+    public void nonCompliant() {
+        TestPublisher
+          .createNoncompliant(TestPublisher.Violation.ALLOW_NULL)
+          .emit("1", "2", null, "3");
+    }
+
+    @Test
+    public void testPublisherInAction() {
+        final TestPublisher<String> testPublisher = TestPublisher.create();
+
+        UppercaseConverter uppercaseConverter = new UppercaseConverter(testPublisher.flux());
+
+        StepVerifier.create(uppercaseConverter.getUpperCase())
+          .then(() -> testPublisher.emit("aA", "bb", "ccc"))
+          .expectNext("AA", "BB", "CCC")
+          .verifyComplete();
+    }
+
+}
+
+class UppercaseConverter {
+    private final Flux<String> source;
+
+    UppercaseConverter(Flux<String> source) {
+        this.source = source;
+    }
+
+    Flux<String> getUpperCase() {
+        return source
+                .map(String::toUpperCase);
+    }
+
+}

spring-5-reactive/src/test/java/com/baeldung/stepverifier/TimeBasedUnitTest.java

@@ -0,0 +1,22 @@
+package com.baeldung.stepverifier;
+
+import org.junit.Test;
+import reactor.core.publisher.Flux;
+import reactor.test.StepVerifier;
+
+import java.time.Duration;
+
+public class TimeBasedUnitTest {
+
+    @Test
+    public void simpleExample() {
+        StepVerifier
+          .withVirtualTime(() -> Flux.interval(Duration.ofSeconds(1)).take(2))
+          .expectSubscription()
+          .expectNoEvent(Duration.ofSeconds(1))
+          .expectNext(0L)
+          .thenAwait(Duration.ofSeconds(1))
+          .expectNext(1L)
+          .verifyComplete();
+    }
+}