CoolOptionalTest.java

package javaprogramming.commonmistakes.java8;

import org.junit.Test;

import java.util.Optional;
import java.util.OptionalDouble;

import static org.hamcrest.CoreMatchers.is;
import static org.hamcrest.CoreMatchers.nullValue;
import static org.junit.Assert.assertFalse;
import static org.junit.Assert.assertThat;

public class CoolOptionalTest {

    @Test(expected = IllegalArgumentException.class)
    public void optional() {
        assertThat(Optional.of(1).get(), is(1));
        assertThat(Optional.ofNullable(null).orElse("A"), is("A"));
        assertFalse(OptionalDouble.empty().isPresent());
        assertThat(Optional.of(1).map(Math::incrementExact).get(), is(2));
        assertThat(Optional.of(1).filter(integer -> integer % 2 == 0).orElse(null), is(nullValue()));
        Optional.empty().orElseThrow(IllegalArgumentException::new);
    }
}