CollectionAssert in jUnit?

Is there a jUnit parallel to NUnit's CollectionAssert?

Using JUnit 4.4 you can use assertThat() together with the Hamcrest code (don't worry, it's shipped with JUnit, no need for an extra .jar) to produce complex self-describing asserts including ones that operate on collections:

import static org.junit.Assert.assertThat;
import static org.junit.matchers.JUnitMatchers.*;
import static org.hamcrest.CoreMatchers.*;

List<String> l = Arrays.asList("foo", "bar");
assertThat(l, hasItems("foo", "bar"));
assertThat(l, not(hasItem((String) null)));
assertThat(l, not(hasItems("bar", "quux")));
// check if two objects are equal with assertThat()

// the following three lines of code check the same thing.
// the first one is the "traditional" approach,
// the second one is the succinct version and the third one the verbose one 
assertEquals(l, Arrays.asList("foo", "bar")));
assertThat(l, is(Arrays.asList("foo", "bar")));
assertThat(l, is(equalTo(Arrays.asList("foo", "bar"))));

Using this approach you will automagically get a good description of the assert when it fails.

Not directly, no. I suggest the use of Hamcrest, which provides a rich set of matching rules which integrates nicely with jUnit (and other testing frameworks)

Take a look at FEST Fluent Assertions. IMHO they are more convenient to use than Hamcrest (and equally powerful, extensible etc) and have better IDE support thanks to fluent interface. See https://github.com/alexruiz/fest-assert-2.x/wiki/Using-fest-assertions

Joachim Sauer's solution is nice but doesn't work if you already have an array of expectations that you want to verify are in your result. This might come up when you already have a generated or constant expectation in your tests that you want to compare a result to, or perhaps you have multiple expectations you expect to be merged in the result. So instead of using matchers you can can just use List::containsAll and assertTrue For Example:

@Test
public void testMerge() {
    final List<String> expected1 = ImmutableList.of("a", "b", "c");
    final List<String> expected2 = ImmutableList.of("x", "y", "z");
    final List<String> result = someMethodToTest(); 

    assertThat(result, hasItems(expected1)); // COMPILE ERROR; DOES NOT WORK
    assertThat(result, hasItems(expected2)); // COMPILE ERROR; DOES NOT WORK

    assertTrue(result.containsAll(expected1));  // works~ but has less fancy
    assertTrue(result.containsAll(expected2));  // works~ but has less fancy
}