Is there a Hamcrest matcher to check that a Collection is neither empty nor null?

Question

Is there a Hamcrest matcher which checks that the argument is neither an empty Collection nor null?

I guess I could always use

both(notNullValue()).and(not(hasSize(0))

but I was wondering whether there is a simpler way and I missed it.

That looks pretty simple to me. Also, it's important that your tests express their intent with as much clarity as possible, and that code is very readable. — skaffman, Dec 15 '14 at 21:41
I don't really know hamcrest, but logically you could check for `size >= 0`, if the API supports such calls. — mike, Dec 15 '14 at 22:45
this question's title asks the opposite of this question's body. To answer the question's title: `assertThat( metadata, either( is( empty() ) ).or( is( nullValue() ) ) );` — Abdull, Sep 09 '16 at 15:42
Not an exact match to your question, but you can `assertTrue(CollectionUtils.isNotEmpty(collectioin))`. `CollectionUtils` is an Apache Commons Lang class. — DwB, Jan 09 '18 at 15:47

eee · Accepted Answer · 2014-12-16T21:27:34.160

You can combine the IsCollectionWithSize and the OrderingComparison matcher:

@Test
public void test() throws Exception {
    Collection<String> collection = ...;
    assertThat(collection, hasSize(greaterThan(0)));
}

For collection = null you get

java.lang.AssertionError: 
Expected: a collection with size a value greater than <0>
    but: was null

For collection = Collections.emptyList() you get

java.lang.AssertionError: 
Expected: a collection with size a value greater than <0>
    but: collection size <0> was equal to <0>

For collection = Collections.singletonList("Hello world") the test passes.

Edit:

Just noticed that the following approch is not working:

assertThat(collection, is(not(empty())));

The more i think about it the more i would recommend a slightly altered version of the statement written by the OP if you want to test explicitly for null.

assertThat(collection, both(not(empty())).and(notNullValue()));

I accepted your answer because I think that both ways shown here, `hasSize(greaterThan(0))` and `both(not(empty())).and(notNullValue())` are a good way. — jhyot, Dec 17 '14 at 12:09
Any reason why I get `1 expectation failed. JSON path images doesn't match. Expected: (an empty collection or null) Actual: null` when i try to check for empty collection or null with your code : `myResponse.body(myArrayAttr, either(empty()).or(nullValue()));` — TheBakker, Jan 03 '18 at 15:11

mike · Answer 2 · 2014-12-15T23:42:21.423

As I posted in the comments, the logical equivalent of collection != null and size != 0 is size > 0, that implies the collection is not null. A simpler way to express size > 0 is there is an (arbitrary) element X in collection. Below a working code example.

import static org.hamcrest.core.IsCollectionContaining.hasItem;
import static org.hamcrest.CoreMatchers.anything;

public class Main {

    public static void main(String[] args) {
        boolean result = hasItem(anything()).matches(null);
        System.out.println(result); // false for null

        result = hasItem(anything()).matches(Arrays.asList());
        System.out.println(result); // false for empty

        result = hasItem(anything()).matches(Arrays.asList(1, 2));
        System.out.println(result); // true for (non-null and) non-empty 
    }
}

score 2 · Answer 3 · answered Apr 17 '19 at 07:09

2

You are welcome to use Matchers:

import static org.hamcrest.MatcherAssert.assertThat;
import static org.hamcrest.Matchers.anyOf;

assertThat(collection, anyOf(nullValue(), empty()));

answered Apr 17 '19 at 07:09

Zon

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Is there a Hamcrest matcher to check that a Collection is neither empty nor null?

3 Answers3