avoid conflict with test_create_collection

tests/database.rs

@@ -61,9 +61,10 @@ fn test_has_collection() {
     let pool     = ClientPool::new(uri, None);
     let client   = pool.pop();
     let database = client.get_database("rust_test");
-    database.get_collection("created_collection").drop().unwrap_or(());
 
-    const COLL_NAME: &'static str = "created_collection";
+    const COLL_NAME: &'static str = "created_collection2";
+
+    database.get_collection(COLL_NAME).drop().unwrap_or(());
 
     let collection = database.create_collection(
         COLL_NAME,
@@ -72,6 +73,4 @@ fn test_has_collection() {
 
     assert_eq!(COLL_NAME, collection.get_name().to_mut());
     assert!(database.has_collection(COLL_NAME).unwrap());
-
-    database.command_simple(doc!{ "drop": COLL_NAME}, None).unwrap();
 }