So stellen Sie mithilfe von Hamcrest und Mockito fest, dass die Oberklassenliste dem Unterklassen-Matcher entspricht

Question

Ich versuche Folgendes zu tun.

final Matcher<SuperClass> matcher1 = Matchers.hasProperty("a", equalTo("b"));
final Matcher<SuperClass> matcher2 = Matchers.hasProperty("c", equalTo("d"));
final Matcher<SuperClass> matchers = Matchers.allOf(matcher1, matcher2);

List<SubClass> list = someStuff();

assertThat(list, everyItem(matchers));

Ich erhalte einen Kompilierungsfehler in der Assert-Zeile. Gibt es eine einfache Möglichkeit, diesen zu beheben?

Answer 1

Option 1:

@SuppressWarnings({"unchecked", "rawtypes"})
@Test public void yourTest() {
    final Matcher<SuperClass> matcher1 = Matchers.hasProperty("a", equalTo("b"));
    final Matcher<SuperClass> matcher2 = Matchers.hasProperty("c", equalTo("d"));
    final Matcher<SuperClass> matchers = Matchers.allOf(matcher1, matcher2);
    List<SubClass> list = someStuff();
    // Note cast to raw type here, corresponding to the suppressed warnings.
    assertThat(list, (Matcher) everyItem(matchers));
}

Option 2:

// These are all of type Matcher<SubClass> instead.
final Matcher<SubClass> matcher1 = Matchers.hasProperty("a", equalTo("b"));
final Matcher<SubClass> matcher2 = Matchers.hasProperty("c", equalTo("d"));
final Matcher<SubClass> matchers = Matchers.allOf(matcher1, matcher2);
List<SubClass> list = someStuff();
assertThat(list, everyItem(matchers));

Warum? Javas Generika-Handhabung ist für Hamcrest zu clever. everyItem(matchers) werde a zurückgeben Matcher<Iterable<SuperClass>>, aber Sie haben kein Iterable<SuperClass>, du hast ein Iterable<SubClass>.Es wäre alles in Ordnung, wenn Ihre Matcher-Methoden tatsächlich eine erzeugen würden Matcher<Iterable<? extends SuperClass>>, aber es ist für Sie fast unmöglich, Java davon zu überzeugen matcher1 Und matcher2 sind miteinander kompatibel.

Answer 2

Generics.

The problem with your code is that you try to assert that a list with type List<SubClass> matches every item of a matcher with type Matcher<SuperClass>.

Even though SuperClass extends SubClass, the assertThat method requires the two to be the same.

So if you can coerce your someStuff() method to return a list of of SuperClass, you should be home free. I.e. something like this

    List<SuperClass> list = someStuff();
    assertThat(list, everyItem(matchers));

would get rid of the compilation error.