Checking that a List is not empty in Hamcrest

Question

I was wondering if anyone knew of a way to check if a List is empty using assertThat   and Matchers   Best way I could see just use JUnit   assertFalse list isEmpty       But I was hoping that there was some way to do this in Hamcrest

User · Answer

Create your own custom IsEmpty TypeSafeMatcher:

Even if the generics problems are fixed in 1.3 the great thing about this method is it works on any class that has an isEmpty() method! Not just Collections!

For example it will work on String as well!

/* Matches any class that has an <code>isEmpty()</code> method
 * that returns a <code>boolean</code> */ 
public class IsEmpty<T> extends TypeSafeMatcher<T>
{
    @Factory
    public static <T> Matcher<T> empty()
    {
        return new IsEmpty<T>();
    }

    @Override
    protected boolean matchesSafely(@Nonnull final T item)
    {
        try { return (boolean) item.getClass().getMethod("isEmpty", (Class<?>[]) null).invoke(item); }
        catch (final NoSuchMethodException e) { return false; }
        catch (final InvocationTargetException | IllegalAccessException e) { throw new RuntimeException(e); }
    }

    @Override
    public void describeTo(@Nonnull final Description description) { description.appendText("is empty"); }
}

User · Answer

Well there s always  assertThat list isEmpty    is false          but I m guessing that s not quite what you meant     Alternatively   assertThat  Collection list  is not empty         empty   is a static in the Matchers class  Note the need to cast the list to Collection  thanks to Hamcrest 1 2 s wonky generics   The following imports can be used with hamcrest 1 3  import static org hamcrest Matchers empty  import static org hamcrest core Is is  import static org hamcrest core IsNot

User · Answer

This is fixed in Hamcrest 1 3  The below code compiles and does not generate any warnings      given List lt String gt  list   new ArrayList lt String gt        then assertThat list  is not empty         But if you have to use older version - instead of bugged empty   you could use   hasSize greaterThan 0    import static org hamcrest number OrderingComparison greaterThan  or import static org hamcrest Matchers greaterThan    Example      given List lt String gt  list   new ArrayList lt String gt        then assertThat list  hasSize greaterThan 0       The most important thing about above solutions is that it does not generate any warnings  The second solution is even more useful if you would like to estimate minimum result size

User · Answer

If you re after readable fail messages  you can do without hamcrest by using the usual assertEquals with an empty list   assertEquals new ArrayList lt  gt  0   yourList     E g  if you run  assertEquals new ArrayList lt  gt  0   Arrays asList  foo    bar      you get  java lang AssertionError Expected     Actual     foo  bar

User · Answer

This works   assertThat list IsEmptyCollection empty

[java] Checking that a List is not empty in Hamcrest

Create your own custom IsEmpty TypeSafeMatcher:

Examples related to java

Examples related to collections

Examples related to junit

Examples related to hamcrest