optional test

app/src/test/java/de/dbubenheim/learning/OptionalTest.java

@@ -1,20 +1,86 @@
 package de.dbubenheim.learning;
 
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 
+import java.io.ByteArrayOutputStream;
+import java.io.PrintStream;
+import java.util.NoSuchElementException;
 import java.util.Optional;
+import java.util.function.Consumer;
 
 import static org.assertj.core.api.AssertionsForClassTypes.assertThat;
+import static org.junit.jupiter.api.Assertions.assertThrows;
 
 public class OptionalTest {
 
-    @Test
-    public void test() {
+    private final PrintStream standardOut = System.out;
+    private final ByteArrayOutputStream outputStreamCaptor = new ByteArrayOutputStream();
+
+    @BeforeEach
+    public void setUp() {
+        System.setOut(new PrintStream(outputStreamCaptor));
+    }
+
+    @AfterEach
+    public void tearDown() {
+        System.setOut(standardOut);
+    }
 
+    @Test
+    public void testIsPresent() {
         Optional<String> optional = Optional.of("123");
         assertThat(optional.isPresent()).isTrue();
         assertThat(optional.get()).isEqualTo("123");
         assertThat(optional).isNotEqualTo(Optional.empty());
+    }
+
+    @Test
+    public void testOfCreatesNewInstance() {
+        Optional<String> optional = Optional.of("123");
+        optional.of("345");
+        assertThat(optional.get()).isEqualTo("123");
+    }
+
+    @Test
+    public void testOrElse() {
+        Optional<String> optional = Optional.empty();
+        assertThat(optional.orElse("Hello")).isEqualTo("Hello");
+    }
 
+    @Test
+    public void testIfPresent() {
+        Consumer<String> s = System.out::println;
+        Optional<String> optional = Optional.of("Hello 123");
+        optional.ifPresent(s);
+        assertThat(outputStreamCaptor.toString().trim()).isEqualTo("Hello 123");
+    }
+
+    @Test
+    public void testGetThrowsException() {
+        Optional<String> optional = Optional.empty();
+        NoSuchElementException exception = assertThrows(NoSuchElementException.class, optional::get);
+        assertThat(exception.getMessage()).isEqualTo("No value present");
+    }
+
+    @Test
+    public void testOfNullThrowsException() {
+        Exception exception = assertThrows(NullPointerException.class, () -> Optional.of(null));
+        assertThat(exception.getMessage()).isNull();
+    }
+
+    @Test
+    public void testOfNullableIsEmpty() {
+        Optional<String> optional = Optional.ofNullable(null);
+        assertThat(optional).isEqualTo(Optional.empty());
+        NoSuchElementException exception = assertThrows(NoSuchElementException.class, optional::get);
+        assertThat(exception.getMessage()).isEqualTo("No value present");
+    }
+
+    @Test
+    public void testOfNullableThrowsException() {
+        Optional<String> optional = Optional.ofNullable("123");
+        assertThat(optional.get()).isEqualTo("123");
     }
 }