How do I assert an Iterable contains elements with a certain property

Question

Assume I want to unit test a method with this signature   List lt MyItem gt  getMyItems      Assume MyItem is a Pojo that has many properties  one of which is  name   accessed via getName     All I care about verifying is that the List lt MyItem gt   or any Iterable  contains two MyItem instances  whose  name  properties have the values  foo  and  bar    If any other properties don t match  I don t really care for the purposes of this test   If the names match  it s a successful test   I would like it to be one-liner if possible  Here is some  pseudo-syntax  of the kind of thing I would like to do     assert listEntriesMatchInAnyOrder myClass getMyItems    property  name    new String    foo    bar       Would Hamcrest be good for this type of thing   If so  what exactly would be the hamcrest version of my pseudo-syntax above

User · Answer

AssertJ provides an excellent feature in extracting() : you can pass Functions to extract fields. It provides a check at compile time.
You could also assert the size first easily.

It would give :

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

Assertions.assertThat(myClass.getMyItems())
          .hasSize(2)
          .extracting(MyItem::getName)
          .containsExactlyInAnyOrder("foo", "bar");

containsExactlyInAnyOrder() asserts that the list contains only these values whatever the order.

To assert that the list contains these values whatever the order but may also contain other values use contains() :

.contains("foo", "bar");

As a side note : to assert multiple fields from elements of a List , with AssertJ we do that by wrapping expected values for each element into a tuple() function :

import static org.assertj.core.api.Assertions;
import static org.assertj.core.groups.Tuple;

Assertions.assertThat(myClass.getMyItems())
          .hasSize(2)
          .extracting(MyItem::getName, MyItem::getOtherValue)
          .containsExactlyInAnyOrder(
               tuple("foo", "OtherValueFoo"),
               tuple("bar", "OtherValueBar")
           );

User · Answer

Thank you  Razvan who pointed me in the right direction   I was able to get it in one line and I successfully hunted down the imports for Hamcrest 1 3   the imports   import static org hamcrest CoreMatchers is  import static org hamcrest Matchers contains  import static org hamcrest MatcherAssert assertThat  import static org hamcrest beans HasPropertyWithValue hasProperty    the code   assertThat  myClass getMyItems    contains      hasProperty  name   is  foo          hasProperty  name   is  bar

User · Answer

AssertJ 3 9 1 supports direct predicate usage in anyMatch method   assertThat collection  anyMatch element - gt  element someProperty satisfiesSomeCondition      This is generally suitable use case for arbitrarily complex condition   For simple conditions I prefer using extracting method  see above  because resulting iterable-under-test might support value verification with better readability  Example  it can provide specialized API such as contains method in Frank Neblung s answer  Or you can call anyMatch on it later anyway and use method reference such as  searchedvalue   equals  Also multiple extractors can be put into extracting method  result subsequently verified using tuple

User · Answer

Try   assertThat myClass getMyItems                              hasItem hasProperty  YourProperty   is  YourValue

User · Answer

Alternatively to hasProperty you can try hamcrest-more-matchers where matcher with extracting function  In your case it will look like  import static com github seregamorph hamcrest MoreMatchers where   assertThat myClass getMyItems    contains      where MyItem  getName  is  quot foo quot          where MyItem  getName  is  quot bar quot         The advantages of this approach are   It is not always possible to verify by field if the value is computed in get-method In case of mismatch there should be a failure message with diagnostics  pay attention to resolved method reference MyItem getName   Expected  iterable containing  Object that matches is  quot foo quot  after call MyItem getName  Object that matches is  quot bar quot  after call MyItem getName       but  item 0  was  quot wrong-name quot    It works in Java 8  Java 11 and Java 14

User · Answer

Assertj is good at this  import static org assertj core api Assertions assertThat       assertThat myClass getMyItems    extracting  quot name quot   contains  quot foo quot    quot bar quot     Big plus for assertj compared to hamcrest is easy use of code completion

User · Answer

Its not especially Hamcrest  but I think it worth to mention here  What I use quite often in Java8 is something like   assertTrue myClass getMyItems   stream   anyMatch item - gt   foo  equals item getName          Edited to Rodrigo Manyari s slight improvement  It s a little less verbose  See comments    It may be a little bit harder to read  but I like the type and refactoring safety  Its also cool for testing multiple bean properties in combination  e g  with a java-like  amp  amp  expression in the filter lambda

User · Answer

As long as your List is a concrete class  you can simply call the contains   method as long as you have implemented your equals   method on MyItem      given     some input     you to complete     when List lt MyItems gt  results   service getMyItems        then assertTrue results contains new MyItem  foo      assertTrue results contains new MyItem  bar        Assumes you have implemented a constructor that accepts the values you want to assert on  I realise this isn t on a single line  but it s useful to know which value is missing rather than checking both at once

[java] How do I assert an Iterable contains elements with a certain property?

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