How can I check both the size and the presence of specific items in a collection using Hamcrest?assertthat hassize

General Discussions
1

In Hamcrest 1.3, I want to assert that a collection meets multiple conditions: it has a minimum size and contains certain items.

Using separate assertions works, but I want a single assertion, e.g., with allOf(). However, combining hasSize() and hasItem() in allOf() leads to a compile-time error.

Is there a way to perform a “single-shot” check for both size and item presence?

2

I ran into this when trying to make my Hamcrest assertions more readable. The trick is that allOf() expects Matchers of the same type, so hasSize() and hasItem() need to be wrapped with Matchers.<Collection<?>>allOf(...) or use both(...).and(...). For example:

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

List<String> myList = Arrays.asList("foo", "bar", "baz");

assertThat(myList, allOf(
    hasSize(3),
    hasItem("foo"),
    hasItem("bar")
));

This works for me and keeps it as a single assertion without splitting it.

3

In my experience, allOf() can be picky if the generics don’t match. One workaround I often use is both(...).and(...) for combining two matchers, and then chain additional assertThats if needed:

> assertThat(myList, both(hasSize(3)).and(hasItem("foo")));
> assertThat(myList, hasItem("bar")); // optional, still readable

It’s not strictly “single-shot” for all conditions, but it avoids compile-time issues with type inference in Hamcrest 1.3. Personally, this style reads nicely in test reports.

4

I ran into the same problem before. Hamcrest’s type system in 1.3 doesn’t like mixing hasSize() and hasItem() directly in allOf() sometimes. What worked for me is wrapping the collection type explicitly:

assertThat(myList, allOf(
    Matchers.<Collection<?>>hasSize(3),
    Matchers.<Collection<?>>hasItem("foo"),
    Matchers.<Collection<?>>hasItem("bar")
));

Adding the <Collection<?>> hint resolves the generics problem and lets you check size and item presence in one assertion.

I found this especially useful for lists of complex objects where I only cared about one property.