How to assert that Set has item with exact property with hamcrest
Solution 1:
Well, you should try to let assertThat do the work for you.
Set<WhateverPropertyTypeYouAreUsing> expectedSet = Collections.singleton( ... create a property object with that id/value);
assertThat(mySet, is(expectedSet))
The restriction here: that assumes that your set contains only that one property value.
Otherwise, you can go for:
assertThat(mySet.contains(someProperty), is(true))
(probably with an additional message to better describe a failing assert).
Prereq: your property class should be implementing equals() in a reasonable manner.