🚧 Gradle 6 - Dependency constraints

gradle-6/build.gradle.kts

@@ -6,9 +6,36 @@ plugins {
 group = "com.baeldung"
 version = "1.0.0"
 
+repositories {
+    mavenCentral()
+}
+
+dependencies {
+    api("io.reactivex.rxjava2:rxjava:2.2.16")
+    implementation("com.google.guava:guava") {
+        version {
+            require("2.0")
+            prefer("28.1-jre")
+            because("Only uses ImmutableList type, so any version since 2.0 will do, but tested with 28.1-jre")
+        }
+    }
+
+    testImplementation("org.junit.jupiter:junit-jupiter-api:5.5.2")
+    testRuntimeOnly("org.junit.jupiter:junit-jupiter-engine:5.5.2")
+}
+
+tasks.compileJava {
+    sourceCompatibility = "1.8"
+    targetCompatibility = "1.8"
+}
+
+tasks.test {
+    useJUnitPlatform()
+}
+
 publishing {
     publications {
-        register("mavenJava", MavenPublication::class) {
+        register<MavenPublication>("mavenJava") {
             from(components["java"])
         }
     }

gradle-6/src/main/java/com/baeldung/gradle/HelloWorld.java

@@ -1,8 +0,0 @@
-package com.baeldung.gradle;
-
-public class HelloWorld {
-
-  public String sayHello() {
-    return "Hello, world!";
-  }
-}

gradle-6/src/main/java/com/baeldung/gradle/RxHelloWorld.java

@@ -0,0 +1,18 @@
+package com.baeldung.gradle;
+
+import com.google.common.collect.ImmutableList;
+import io.reactivex.Observable;
+import java.util.List;
+
+/** Demonstrates a library type that returns an RxJava type. */
+public class RxHelloWorld {
+
+  /** @return an {@link Observable} that emits events "hello" and "world" before completing. */
+  public static Observable<String> hello() {
+    // Guava ImmutableList class is an implementation detail.
+    List<String> values = ImmutableList.of("hello", "world");
+    return Observable.fromIterable(values);
+  }
+
+  private RxHelloWorld() {}
+}

gradle-6/src/test/java/com/baeldung/gradle/RxHelloWorldUnitTest.java

@@ -0,0 +1,14 @@
+package com.baeldung.gradle;
+
+import static com.baeldung.gradle.RxHelloWorld.hello;
+
+import org.junit.jupiter.api.Test;
+
+/** Unit test for {@link RxHelloWorld}. */
+final class RxHelloWorldUnitTest {
+
+  @Test
+  void it_emits_hello_world_values() {
+    hello().test().assertValues("hello", "world").assertComplete();
+  }
+}