Added javadoc and test for Optionals utility class

core/src/main/java/cz/o2/proxima/util/Optionals.java

@@ -17,8 +17,18 @@
 
 import java.util.Optional;
 
+/**
+ * Utility class for manipulation with {@link Optional}
+ */
 public class Optionals {
-
+  /**
+   * Get value from Optional or throw IllegalArgumentException
+   *
+   * @param optional Optional object
+   * @param <T>      Generic type Optional
+   * @return T value from Optional
+   * @throws IllegalArgumentException in case of empty value
+   */
   public static <T> T get(Optional<T> optional) {
     return optional.orElseThrow(() ->
         new IllegalArgumentException("Provided optional is empty."));

core/src/test/java/cz/o2/proxima/util/OptionalsTest.java

@@ -0,0 +1,39 @@
+/**
+ * Copyright 2017-2019 O2 Czech Republic, a.s.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package cz.o2.proxima.util;
+
+import org.junit.Test;
+
+import java.util.Optional;
+
+import static org.junit.Assert.assertEquals;
+
+/**
+ * Tests for utility class {@link Optionals}
+ */
+public class OptionalsTest {
+
+  @Test
+  public void testGet() {
+    String foo = "bar";
+    assertEquals(foo, Optionals.get(Optional.of(foo)));
+  }
+
+  @Test(expected = IllegalArgumentException.class)
+  public void testGetFromEmpty() {
+    Optionals.get(Optional.empty());
+  }
+}