Is there any Hamcrest Matcher for java.util.Optional?

Question

I am looking for a Hamcrest Matcher to unit test methods that return a java.util.Optional type. Something like:

    @Test
    public void get__Null(){

        Optional<Element> element = Element.get(null);      
        assertThat( sasi , isEmptyOptional());
    }

    @Test
    public void get__GetCode(){

        Optional<Element> element = Element.get(MI_CODE);       
        assertThat( sasi , isOptionalThatMatches(allOf(hasproperty("code", MI_CODE),
                                                       hasProperty("id",   notNullValue())));
    }

Is there any implementation available throw the Maven Repository?

Answer 1

Presently Java Hamcrest is using 1.6 version and is integrated with many projects that use older version of Java.

So the features related to Java 8 will be added in future versions that are Java 8 compatible. The solution proposed was to have an extension library that supports it, so that anyone who needs can use extension library.

I am the author of Hamcrest Optional and it is now available on Maven central.

Example: Checking if the Optional contains a string starting with some value

import static com.github.npathai.hamcrestopt.OptionalMatchers.hasValue;
import static org.hamcrest.Matchers.startsWith;

Optional<String> optional = Optional.of("dummy value");
assertThat(optional, hasValue(startsWith("dummy")));

Answer 2

The Hamcrest Optional from Narendra Pathai does great job indeed.

import static com.github.npathai.hamcrestopt.OptionalMatchers.isEmpty;
import static com.github.npathai.hamcrestopt.OptionalMatchers.isPresent;
import static com.github.npathai.hamcrestopt.OptionalMatchers.isPresentAnd;
import static com.github.npathai.hamcrestopt.OptionalMatchers.isPresentAndIs;
import static org.hamcrest.Matchers.startsWith;
import static org.junit.Assert.assertThat;
import static org.junit.Assert.assertTrue;

  @Test
  public void testOptionalValue() {
    Optional<String> option = Optional.of("value");
    assertTrue(option.isPresent()); // the old-fashioned, non-diagnosable assertion
    assertThat(option, isPresent());
    assertThat(option, isPresentAndIs("value"));
    assertThat(option, isPresentAnd(startsWith("v")));
    assertThat(option, isEmpty()); // fails
  }

The last assertion above fails and produces nice diagnosable message:

java.lang.AssertionError: 
Expected: is <Empty>
     but: had value "value"

Available on Maven :

<dependency>
  <groupId>com.github.npathai</groupId>
  <artifactId>hamcrest-optional</artifactId>
  <version>2.0.0</version>
  <scope>test</scope>
</dependency>