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

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

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  lt code gt isEmpty   lt  code gt  method    that returns a  lt code gt boolean lt  code gt      public class IsEmpty lt T gt  extends TypeSafeMatcher lt T gt         Factory     public static  lt T gt  Matcher lt T gt  empty                 return new IsEmpty lt T gt                 Override     protected boolean matchesSafely  Nonnull final T item                try   return  boolean  item getClass   getMethod  quot isEmpty quot    Class lt   gt     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  quot is empty quot

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

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

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

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