minor: ensure index tests

Author: banker

test/collection_test.rb

@@ -578,13 +578,16 @@ def test_ensure_index
     @@test.ensure_index([["x", Mongo::ASCENDING]])
     assert @@test.index_information.keys.include? "x_1"
 
+    @@test.ensure_index([["type", 1], ["date", -1]])
+    assert @@test.index_information.keys.include? "type_1_date_-1"
+
     @@test.drop_index("x_1")
-    assert_equal 2, @@test.index_information.keys.count
+    assert_equal 3, @@test.index_information.keys.count
     @@test.drop_index("x_-1")
-    assert_equal 1, @@test.index_information.keys.count
-
-    @@test.ensure_index([["x", Mongo::DESCENDING]], {}) #should work as not cached.
     assert_equal 2, @@test.index_information.keys.count
+
+    @@test.ensure_index([["x", Mongo::DESCENDING]], {})
+    assert_equal 3, @@test.index_information.keys.count
     assert @@test.index_information.keys.include? "x_-1"
 
     # Make sure that drop_index expires cache properly