Add map(…) and flatMap(…) to OptionalAssert #751
Description
Summary
If you're dealing with Optionals whose values return Optionals, you end u with a lot of nesting. It would be cool if these could be flattened out like this:
Example
Optiona<Foo> foo = Optional.of(foo);
assertThat(foo).hasValueSatisfying(it -> {
assertThat(it.methodReturningAnOptional()).hasValueSatisfying(inner -> {
assertThat(inner.methodReturningNoOptional()).isEqualTo(reference);
}
}Note, how you constantly have to nest expressions and also rewrap the values obtained from the method call into new asserts.
It would be cool if one could rather write this instead:
assertThat(foo)
.flatMap(it -> it.methodReturningAnOptional())
.map(it -> it.methodReturningNoOptional())
.isEqualTo(reference);I currently have this custom assert class in my code to achieve this:
public class OptionalAssert<T> extends AbstractAssert<OptionalAssert<T>, Optional<T>> {
public OptionalAssert(Optional<T> actual) {
super(actual, OptionalAssert.class);
}
public static <T> OptionalAssert<T> optionalAssertThat(Optional<T> optional) {
return new OptionalAssert<T>(optional);
}
public <S> OptionalAssert<S> flatMap(Function<T, Optional<S>> function) {
Assertions.assertThat(actual).isPresent();
return optionalAssertThat(actual.flatMap(function));
}
public <S> AbstractObjectAssert<?, S> map(Function<T, S> function) {
Assertions.assertThat(actual).isPresent();
return Assertions.assertThat(actual.map(function).orElseThrow(() -> new IllegalStateException()));
}
}I guess that can be improved to report good error messages in case of a flat map step producing an empty Optional, but it does the trick for me now.