BAEL-949 java9 optional test (#1960)

core-java-9/src/test/java/com/baeldung/java9/Java9OptionalTest.java

@@ -0,0 +1,85 @@
+package com.baeldung.java9;
+
+public class Java9OptionalTest {
+    @Test
+    public void givenOptionalOfSome_whenToStream_thenShouldTreatItAsOneElementStream() {
+        //given
+        Optional<String> value = Optional.of("a");
+
+        //when
+        List<String> collect = value.stream().map(String::toUpperCase).collect(Collectors.toList());
+
+        //then
+        assertThat(collect).hasSameElementsAs(List.of("A"));
+    }
+
+    @Test
+    public void givenOptionalOfNone_whenToStream_thenShouldTreatItAsZeroElementStream() {
+        //given
+        Optional<String> value = Optional.empty();
+
+        //when
+        List<String> collect = value.stream().map(String::toUpperCase).collect(Collectors.toList());
+
+        //then
+        assertThat(collect).isEmpty();
+    }
+
+    @Test
+    public void givenOptional_whenPresent_thenShouldExecuteProperCallback() {
+        //given
+        Optional<String> value = Optional.of("properValue");
+        AtomicInteger successCounter = new AtomicInteger(0);
+        AtomicInteger onEmptyOptionalCounter = new AtomicInteger(0);
+
+        //when
+        value.ifPresentOrElse((v) -> successCounter.incrementAndGet(), onEmptyOptionalCounter::incrementAndGet);
+
+        //then
+        assertThat(successCounter.get()).isEqualTo(1);
+        assertThat(onEmptyOptionalCounter.get()).isEqualTo(0);
+    }
+
+    @Test
+    public void givenOptional_whenNotPresent_thenShouldExecuteProperCallback() {
+        //given
+        Optional<String> value = Optional.empty();
+        AtomicInteger successCounter = new AtomicInteger(0);
+        AtomicInteger onEmptyOptionalCounter = new AtomicInteger(0);
+
+        //when
+        value.ifPresentOrElse((v) -> successCounter.incrementAndGet(), onEmptyOptionalCounter::incrementAndGet);
+
+        //then
+        assertThat(successCounter.get()).isEqualTo(0);
+        assertThat(onEmptyOptionalCounter.get()).isEqualTo(1);
+    }
+
+    @Test
+    public void givenOptional_whenPresent_thenShouldTakeAValueFromIt() {
+        //given
+        String expected = "properValue";
+        Optional<String> value = Optional.of(expected);
+        Optional<String> defaultValue = Optional.of("default");
+
+        //when
+        Optional<String> result = value.or(() -> defaultValue);
+
+        //then
+        assertThat(result.get()).isEqualTo(expected);
+    }
+
+    @Test
+    public void givenOptional_whenEmpty_thenShouldTakeAValueFromOr() {
+        //given
+        String defaultString = "default";
+        Optional<String> value = Optional.empty();
+        Optional<String> defaultValue = Optional.of(defaultString);
+
+        //when
+        Optional<String> result = value.or(() -> defaultValue);
+
+        //then
+        assertThat(result.get()).isEqualTo(defaultString);
+    }
+}