Fix tests and operation cache

src/MetagraphOptimization.jl

@@ -6,7 +6,7 @@ export make_node, make_edge, insert_node, insert_edge, is_entry_node, is_exit_no
 export NodeFusion, NodeReduction, NodeSplit, push_operation!, pop_operation!, can_pop, reset_graph!, get_operations
 export import_txt
 
-export ==, in, show
+export ==, in, show, isempty, delete!
 
 export bytes_to_human_readable
 
@@ -15,6 +15,8 @@ import Base.show
 import Base.==
 import Base.in
 import Base.copy
+import Base.isempty
+import Base.delete!
 
 
 include("tasks.jl")