Fix outstanding test failure.

Author: sageserpent-open

src/main/scala/scala/collection/decorators/MapDecorator.scala

@@ -59,16 +59,16 @@ class MapDecorator[C, M <: IsMap[C]](coll: C)(implicit val map: M) {
     */
   def mergeByKeyWith[W, X, That](other: Map[map.K, W])(f: PartialFunction[(Option[map.V], Option[W]), X])(implicit bf: BuildFrom[C, (map.K, X), That]): That = {
     val b = bf.newBuilder(coll)
-    val traversed = mutable.Set.empty[W]
+    val traversed = mutable.Set.empty[map.K]
     val pf = f.lift
     for {
       (k, v) <- map(coll)
-      x <- pf(other.get(k).fold[(Option[map.V], Option[W])]((Some(v), None)){ w => traversed += w; (Some(v), Some(w)) })
+      x <- pf(other.get(k).fold[(Option[map.V], Option[W])]((Some(v), None)){ w => traversed += k; (Some(v), Some(w)) })
     } {
       b += k -> x
     }
     for {
-      (k, w) <- other if !traversed(w)
+      (k, w) <- other if !traversed(k)
       x <- pf((None, Some(w)))
     } {
       b += k -> x

src/test/scala/scala/collection/decorators/MapDecoratorTest.scala

@@ -130,7 +130,7 @@ class MapDecoratorTest {
           .sorted
           .sameElements(theirChanges.mergeByKey(ourChanges).values.toList.sorted))
 
-      Assert.assertEquals(ourChanges.mergeByKey(theirChanges).keySet, theirChanges
+      Assert.assertEquals("Expect reflexivity on an outer join in terms of the keys.", ourChanges.mergeByKey(theirChanges).keySet, theirChanges
         .mergeByKey(ourChanges)
         .keys)
     }
@@ -153,22 +153,22 @@ class MapDecoratorTest {
 
       ourChanges.mergeByKey(theirChangesRedux)
 
-      Assert.assertEquals("Expect all the keys to appear in an outer join, but they don't.", ourChanges.mergeByKey(theirChangesRedux).keys, allKeys)
+      Assert.assertEquals("Expect all the keys to appear in an outer join.", ourChanges.mergeByKey(theirChangesRedux).keys, allKeys)
 
       theirChangesRedux.mergeByKey(ourChanges)
 
-      Assert.assertEquals("Expect all the keys to appear in an outer join, and they do, good.", theirChangesRedux.mergeByKey(ourChanges).keys, allKeys)
+      Assert.assertEquals("Expect all the keys to appear in an outer join.", theirChangesRedux.mergeByKey(ourChanges).keys, allKeys)
 
       Assert.assertTrue("Expect the same associated values to appear in the join taken either way around, albeit swapped around and not necessarily in the same key order.",
         ourChanges
-        .mergeByKey(theirChangesRedux)
-        .values
-        .map(_.swap)
-        .toList
-        .sorted
-        .sameElements(theirChangesRedux.mergeByKey(ourChanges).values.toList.sorted))
-
-      Assert.assertEquals("Expect these to be equal, but they aren't.", ourChanges.mergeByKey(theirChangesRedux).keySet, theirChangesRedux
+          .mergeByKey(theirChangesRedux)
+          .values
+          .map(_.swap)
+          .toList
+          .sorted
+          .sameElements(theirChangesRedux.mergeByKey(ourChanges).values.toList.sorted))
+
+      Assert.assertEquals("Expect reflexivity on an outer join in terms of the keys.", ourChanges.mergeByKey(theirChangesRedux).keySet, theirChangesRedux
         .mergeByKey(ourChanges)
         .keys)
     }