How to use custom comparator / diff in PAssert of PCollection

Question

I have a code similar to the one below transforming a PCollections of Protocol Buffer messages. Because some of them are pretty big I want to not only test it using for equality but also print where's the difference.

I want to use https://google.github.io/truth/fuzzy tests which offer to print a difference.

PCollection<PbMsg1> p1 = ...;
List<PbMsg1> p2 = loadFixture();

PAssert.that(p1).containsInAnyOrder(output.getUserReqList());

The question is either:

1. How to use custom diff / compare function in PAssert?
2. How to convert from a PCollection to List?

Answer 1

I know this may be too old now, but I found a convoluted way of solving it.. I found a way by writing a custom serializable function which acts a a satisfaction function.

For your use case write the PAssert as below.

PAssert.that(p1).satisfies(PCollectionSatisfies.forExpectedList(p2));

and implement the Satisfaction function as

public class PCollectionSatisfies {

  public static <T> SerializableFunction<Iterable<T>, Void> forExpectedList(ImmutableList<T> expected) {

    return (SerializableFunction<Iterable<T>, Void>)
        input -> {
          Truth.assertThat(input).containsExactlyElementsIn(expected).inOrder();
          return null;
        };
  }

  public static <T> SerializableFunction<T, Void> forSingleton(T expected) {
    return (SerializableFunction<T, Void>)
        input -> {
          Truth.assertThat(input).isEqualTo(expected);
          return null;
        };
  }
}

Hope that helps.