Is there a Hamcrest "for each" Matcher that asserts all elements of a Collection or Iterable match a single specific Matcher?

Question

Given a Collection or Iterable of items, is there any Matcher (or combination of matchers) that will assert every item matches a single Matcher?

For example, given this item type:

public interface Person {
    public String getGender();
}

I'd like to write an assertion that all items in a collection of Persons have a specific gender value. I'm thinking something like this:

Iterable<Person> people = ...;
assertThat(people, each(hasProperty("gender", "Male")));

Is there any way to do this without writing the each matcher myself?

Probably you can use the everyItem Matcher: http://junit.sourceforge.net/javadoc/org/junit/matchers/JUnitMatchers.html — René Winkler, Mar 04 '15 at 16:54

Sotirios Delimanolis · Accepted Answer · 2015-03-04T18:52:48.940

104

Use the Every matcher.

import org.hamcrest.beans.HasPropertyWithValue;
import org.hamcrest.core.Every;
import org.hamcrest.core.Is;
import org.junit.Assert;

Assert.assertThat(people, (Every.everyItem(HasPropertyWithValue.hasProperty("gender", Is.is("male")))));

Hamcrest also provides Matchers#everyItem as a shortcut to that Matcher.

Full example

@org.junit.Test
public void method() throws Exception {
    Iterable<Person> people = Arrays.asList(new Person(), new Person());
    Assert.assertThat(people, (Every.everyItem(HasPropertyWithValue.hasProperty("gender", Is.is("male")))));
}

public static class Person {
    String gender = "male";

    public String getGender() {
        return gender;
    }

    public void setGender(String gender) {
        this.gender = gender;
    }
}

edited Mar 04 '15 at 18:52

answered Mar 04 '15 at 16:59

Sotirios Delimanolis

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It seems that generics is causing problems. I'm getting a compilation problem because `assertThat()` expects argument types `T, Matcher` but it's getting `Iterable, Matcher>` – E-Riz Mar 04 '15 at 18:11
@E-Riz I've updated with a full example. If yours is different, please edit your question to include it. – Sotirios Delimanolis Mar 04 '15 at 18:53
1

You example still has the generics-related compilation problem, but only when compiled against JDK 7; with JDK 8 it compiles fine. I wasn't aware that the generics spec changed between 7 and 8 but apparently they realized the compiler was being stupid and fixed it. – E-Riz Mar 04 '15 at 19:04
2

To get it to compile for Java 7, I had to declare the hasProperty Matcher like this: `HasPropertyWithValue.hasProperty("gender", is("Male"))` which pretty much destroys the readability improvements that Hamcrest is supposed to provide :-( – E-Riz Mar 04 '15 at 19:08
1

And beyond that, woohaaa, reflection and by-string access. I find that super-ugly. I would rather manually iterate the collection and assertThat() on Person::getGender() than ... – GhostCat Aug 02 '17 at 08:53

score 2 · Answer 2 · answered Apr 29 '19 at 14:23

2

IMHO this is much more readable:

people.forEach(person -> Assert.assertThat(person.getGender()), Is.is("male"));

answered Apr 29 '19 at 14:23

Markus

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15

This is anti-pattern. Asserts should not be placed inside a loop. – Petar Mitrovic Jan 23 '20 at 10:58
@PetarMitrovic Why Asserts should not be placed inside loop? – Raghu Oct 22 '20 at 05:05
4

Simply put you won't be able to get the whole picture about the failing asserts as the test runner would exit as soon as it encounters the first failing one. – Petar Mitrovic Oct 23 '20 at 13:08

score -2 · Answer 3 · answered May 03 '21 at 13:24

-2

More readable than the approved answer and no separate assertions in a loop:

import static org.assertj.core.api.Assertions.assertThat;

assertThat(people).allMatch((person) -> {
  return person.gender.equals("male");
});

answered May 03 '21 at 13:24

xaviert

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1

but that is not Hamcrest – andresp Jan 07 '22 at 14:09

Is there a Hamcrest "for each" Matcher that asserts all elements of a Collection or Iterable match a single specific Matcher?

3 Answers3

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