Implement the As protocol for two field entities

Previous commits reported that `month-day` did not implement the `As`
protocol.

This commit implements this protocol for `month-day` and for
`year-month`.

Author: Larry Jones

src/java_time/single_field.clj

@@ -163,7 +163,10 @@
          (single-after? [d# o#]
            (.isAfter d# o#))
          (single-before? [d# o#]
-           (.isBefore d# o#))))))
+           (.isBefore d# o#))
+         jt.c/As
+         (as* [o# k#]
+            (jt.c/value (jt.c/property o# k#)))))))
 
 (enumerated-entity DayOfWeek
   "Returns the `DayOfWeek` for the given day keyword name (e.g. `:monday`),

test/java_time_test.clj

@@ -644,6 +644,16 @@
       (is (= 1 (j/as (j/local-date 2015 1 1) :day-of-month)))
       (is (= 2015 (j/as (j/local-date 2015 1 1) :year))))
 
+    (testing "temporal-accessor"
+      (let [month-day-under-test (j/month-day 3 31)]
+       (is (= 3 (j/as month-day-under-test :month-of-year)))
+       (is (= 31 (j/as month-day-under-test :day-of-month)))
+       (is (thrown? Exception (j/as month-day-under-test :year))))
+      (let [year-month-under-test (j/year-month 2018 3)]
+       (is (= 2018 (j/as year-month-under-test :year)))
+       (is (= 3 (j/as year-month-under-test :month-of-year)))
+       (is (thrown? Exception (j/as year-month-under-test :day-of-month)))))
+
     (testing "multiple"
       (is (= [2015 1 1] (j/as (j/local-date 2015 1 1) :year :month-of-year :day-of-month))))