Support for java 8 Predicates

[sta-szek]

Summary

It would be nice to have support for java 8 predicates.
Assertions should allow for testing them instead of testing everyone separetly.

Real life use case / example

Good:

//given
acceptedValues = Lists.newArrayList("a","b")

//when
final Predicate<String> predicate = Predicate.create(acceptedValues);

//then
assertThat(predicate).accepts("a")
                     .accepts("b")
                     .doesNotAccept("c")
                     .accepts(Lists.newArrayList("a","b"))
                     .doesNotAccept(Lists.newArrayList("c","d"));

Not good:

//given
acceptedValues = Lists.newArrayList("a","b")

//when
final Predicate<String> predicate = Predicate.create(acceptedValues);
boolean result1 = predicate.test("a");
boolean result2 = predicate.test("b");
boolean result3 = predicate.test("c");
boolean result4 = predicate.test("d");

//then
assertThat(result1).isTrue();
assertThat(result2).isTrue();
assertThat(result3).isFalse();
assertThat(result4).isFalse();

Java 8 specific ?

YES

[joel-costigliola]

Good idea, I would just use matches instead of accepts and matchAll for collection/array.

[filiphr]

@joel-costigliola I am willing to work on this if no one is. I already have some idea about how to do it.

I just have one question, do we also need the other predicates (IntPredicate, LongPredicate, DoublePredicate).

[joel-costigliola]

@filiphr that would be great ! regarding your question I would say yes (we have the same thing with Optional).

[joel-costigliola]

@filiphr do you prefer assertThat(predicate).accepts("a") or assertThat(predicate).matches("a") ?
I'm having second thoughts and contradict my previous comment) as it is correct to say that a value matches a predicate but not the other way around.

[filiphr]

@joel-costigliola I think that accepts is more suitable in this situation. You are correct.

[joel-costigliola]

accepts accepted then :)

[filiphr]

While doing the changes to accepts something else came to my mind. Regarding the error factories, I am reusing some which were already there, like ShouldMatch, and I am also reusing the Iterables#assertAllMatch is that acceptable?

[joel-costigliola]

No, I think this will be confusing, if you assert that the predicate should accept a value and it does not then the problem is on the predicate not the value, I would use a message like:

Expecting given predicate to accept <value> but did not.

where given is replaced by predicate description when provided.
Feel free to suggest a better error message ...

[filiphr]

I will modify the error messages so it is better to understand. Will probably do something in the Iterables as the logic is the same for the assertion

[joel-costigliola]

👍

[jangalinski]

Nice feature. I know discussion is over, but I just have to add my two c:

I am used to the FunctionalInterfaces, so "accept" to automatically indicates a Consumer. Working with predicates I would expect "tests" (and doesNotTest).

[joel-costigliola]

well if you write assertThat(predicate).test("a") it is not clear that it means assertThat(predicate).testToTrue("a") as predicate.test("a") can return true or false.

assertThat(predicate).evaluateToTrue("a") would be closer to the java api wording but a little bit too long to my taste.

[sta-szek]

or according to predicate's 'test' method it could be:
assertThat(predicate).passes("a")
assertThat(predicate).passesOn("a")
assertThat(predicate).willPass("a")
assertThat(predicate).isPassing("a") ?

[joel-costigliola]

I kind of like assertThat(predicate).isTrueFor("a") but I still have a slight preference for accepts.

[jangalinski]

+1 for "isTrueFor"