FizzBuzzStream.java

package de.gtrefs.fizzbuzz.more;

import javaslang.collection.Stream;
import javaslang.test.Arbitrary;
import javaslang.test.Property;
import org.junit.jupiter.api.Test;

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

public class FizzBuzzStream {

    @Test
    public void generate_a_stream(){
        assertThat(fizzBuzz()).isNotNull();
    }

    @Test
    public void generate_a_stream_with_third_element_being_Fizz(){
        nth_element_should_be(3,"Fizz");
    }

    @Test
    public void generate_a_stream_with_fifth_element_being_Buzz(){
        nth_element_should_be(5,"Buzz");
    }

    @Test
    public void generate_a_stream_with_first_element_being_1(){
        nth_element_should_be(1,"1");
    }

    private void nth_element_should_be(Integer n, String result){
        assertThat(fizzBuzz().drop(n-1).head()).isEqualTo(result);
    }

    @Test
    public void generate_a_stream_with_every_third_element_being_Fizz() {
        final Arbitrary<Integer> multiplesOf3 = Arbitrary.integer()
                                                         .filter(i -> i > 0)
                                                         .filter(i -> i % 3 == 0);

        Property.def("Every third element must contain Fizz")
                .forAll(multiplesOf3)
                .suchThat(i -> fizzBuzz().drop(i - 1).head().contains("Fizz"))
                .check()
                .assertIsSatisfied();
    }

    private Stream<String> fizzBuzz(){
        return Stream.of("","","Fizz").cycle()
                     .zip(Stream.of("","","","","Buzz").cycle())
                     .zip(Stream.from(1))
                     .map(flatten());
    }

    private Function<Tuple2<Tuple2<String, String>, Integer>, String> flatten() {
        return t -> {
            final String fizzBuzz = t._1._1 + t._1._2;
            return fizzBuzz.isEmpty()?t._2.toString():fizzBuzz;
        };
    }
}