diff --git a/src/lib_shell/chain.ml b/src/lib_shell/chain.ml
index 9cc05acb7..f168d71af 100644
--- a/src/lib_shell/chain.ml
+++ b/src/lib_shell/chain.ml
@@ -39,6 +39,7 @@ type data = State.chain_data = {
   current_mempool: Mempool.t ;
   live_blocks: Block_hash.Set.t ;
   live_operations: Operation_hash.Set.t ;
+  test_chain: Chain_id.t option ;
 }
 
 let data chain_state =
@@ -87,6 +88,7 @@ let locked_set_head chain_store data block =
                current_mempool = Mempool.empty ;
                live_blocks ;
                live_operations ;
+               test_chain = None ;
              }
 
 let set_head chain_state block =
diff --git a/src/lib_shell/chain.mli b/src/lib_shell/chain.mli
index 481168c8e..13bd60391 100644
--- a/src/lib_shell/chain.mli
+++ b/src/lib_shell/chain.mli
@@ -23,6 +23,7 @@ type data = {
   current_mempool: Mempool.t ;
   live_blocks: Block_hash.Set.t ;
   live_operations: Operation_hash.Set.t ;
+  test_chain: Chain_id.t option ;
 }
 
 (** Reading atomically all the chain data. *)
diff --git a/src/lib_shell/node.ml b/src/lib_shell/node.ml
index ef0805402..1a19ce319 100644
--- a/src/lib_shell/node.ml
+++ b/src/lib_shell/node.ml
@@ -127,14 +127,13 @@ let create { genesis ; store_root ; context_root ;
     chain_validator_limits =
   init_p2p p2p_params >>=? fun p2p ->
   State.read
-    ~store_root ~context_root ?patch_context () >>=? fun state ->
+    ~store_root ~context_root ?patch_context genesis >>=? fun (state, mainchain_state) ->
   let distributed_db = Distributed_db.create state p2p in
   Validator.create state distributed_db
     peer_validator_limits
     block_validator_limits
     prevalidator_limits
     chain_validator_limits >>= fun validator ->
-  may_create_chain state genesis >>= fun mainchain_state ->
   Validator.activate validator
     ?max_child_ttl mainchain_state >>= fun mainchain_validator ->
   let shutdown () =
diff --git a/src/lib_shell/state.ml b/src/lib_shell/state.ml
index 01d1ec508..818747d04 100644
--- a/src/lib_shell/state.ml
+++ b/src/lib_shell/state.ml
@@ -23,6 +23,7 @@ end
 type global_state = {
   global_data: global_data Shared.t ;
   protocol_store: Store.Protocol.store Shared.t ;
+  main_chain: Chain_id.t ;
 }
 
 and global_data = {
@@ -60,6 +61,7 @@ and chain_data = {
   current_mempool: Mempool.t ;
   live_blocks: Block_hash.Set.t ;
   live_operations: Operation_hash.Set.t ;
+  test_chain: Chain_id.t option ;
 }
 
 and block = {
@@ -242,6 +244,12 @@ module Chain = struct
   type t = chain_state
   type chain_state = t
 
+  let main { main_chain } = main_chain
+  let test chain_state =
+    read_chain_data chain_state begin fun _ chain_data ->
+      Lwt.return chain_data.test_chain
+    end
+
   let allocate
       ~genesis ~faked_genesis_hash ~expiration ~allow_forked_chain
       ~current_head
@@ -258,6 +266,7 @@ module Chain = struct
         current_mempool = Mempool.empty ;
         live_blocks = Block_hash.Set.singleton genesis.block ;
         live_operations = Operation_hash.Set.empty ;
+        test_chain = None ;
       } ;
       chain_data_store ;
     }
@@ -367,12 +376,18 @@ module Chain = struct
       locked_read_all state data
     end
 
-  let get state id =
+  let get_exn state id =
     Shared.use state.global_data begin fun data ->
-      try return (Chain_id.Table.find data.chains id)
-      with Not_found -> fail (Unknown_chain id)
+      Lwt.return (Chain_id.Table.find data.chains id)
     end
 
+  let get state id =
+    Lwt.catch
+      (fun () -> get_exn state id >>= return)
+      (function
+        | Not_found -> fail (Unknown_chain id)
+        | exn -> Lwt.fail exn)
+
   let all state =
     Shared.use state.global_data begin fun { chains } ->
       Lwt.return @@
@@ -706,6 +721,9 @@ let fork_testchain block protocol expiration =
     } in
     Chain.locked_create block.chain_state.global_state data
       chain_id ~expiration genesis commit >>= fun chain ->
+    update_chain_data block.chain_state begin fun _ chain_data ->
+      Lwt.return (Some { chain_data with test_chain = Some chain.chain_id }, ())
+    end >>= fun () ->
     return chain
   end
 
@@ -793,11 +811,16 @@ module Current_mempool = struct
 
 end
 
+let may_create_chain state chain genesis =
+  Chain.get state chain >>= function
+  | Ok chain -> Lwt.return chain
+  | Error _ -> Chain.create state genesis
+
 let read
     ?patch_context
     ~store_root
     ~context_root
-    () =
+    genesis =
   Store.init store_root >>=? fun global_store ->
   Context.init ?patch_context ~root:context_root >>= fun context_index ->
   let global_data = {
@@ -805,12 +828,15 @@ let read
     global_store ;
     context_index ;
   } in
+  let main_chain = Chain_id.of_block_hash genesis.Chain.block in
   let state = {
     global_data = Shared.create global_data ;
     protocol_store = Shared.create @@ Store.Protocol.get global_store ;
+    main_chain ;
   } in
   Chain.read_all state >>=? fun () ->
-  return state
+  may_create_chain state main_chain genesis >>= fun main_chain_state ->
+  return (state, main_chain_state)
 
 let close { global_data } =
   Shared.use global_data begin fun { global_store } ->
diff --git a/src/lib_shell/state.mli b/src/lib_shell/state.mli
index 18fc33a07..a419d20a8 100644
--- a/src/lib_shell/state.mli
+++ b/src/lib_shell/state.mli
@@ -19,18 +19,6 @@
 type t
 type global_state = t
 
-(** Read the internal state of the node and initialize
-    the databases. *)
-val read:
-  ?patch_context:(Context.t -> Context.t Lwt.t) ->
-  store_root:string ->
-  context_root:string ->
-  unit ->
-  global_state tzresult Lwt.t
-
-val close:
-  global_state -> unit Lwt.t
-
 (** {2 Network} ************************************************************)
 
 (** Data specific to a given chain (e.g the main chain or the current
@@ -58,6 +46,10 @@ module Chain : sig
 
   (** Look up for a chain by the hash of its genesis block. *)
   val get: global_state -> Chain_id.t -> chain_state tzresult Lwt.t
+  val get_exn: global_state -> Chain_id.t -> chain_state Lwt.t
+
+  val main: global_state -> Chain_id.t
+  val test: chain_state -> Chain_id.t option Lwt.t
 
   (** Returns all the known chains. *)
   val all: global_state -> chain_state list Lwt.t
@@ -174,6 +166,7 @@ type chain_data = {
   current_mempool: Mempool.t ;
   live_blocks: Block_hash.Set.t ;
   live_operations: Operation_hash.Set.t ;
+  test_chain: Chain_id.t option ;
 }
 
 val read_chain_data:
@@ -224,3 +217,15 @@ module Current_mempool : sig
       not the provided one. *)
 
 end
+
+(** Read the internal state of the node and initialize
+    the databases. *)
+val read:
+  ?patch_context:(Context.t -> Context.t Lwt.t) ->
+  store_root:string ->
+  context_root:string ->
+  Chain.genesis ->
+  (global_state * Chain.t) tzresult Lwt.t
+
+val close:
+  global_state -> unit Lwt.t
diff --git a/src/lib_shell/test/test_locator.ml b/src/lib_shell/test/test_locator.ml
index 3d4cd3ede..f9d0cb19c 100644
--- a/src/lib_shell/test/test_locator.ml
+++ b/src/lib_shell/test/test_locator.ml
@@ -54,10 +54,11 @@ let incr_fitness fitness =
 let init_chain base_dir : State.Chain.t Lwt.t =
   let store_root = base_dir // "store" in
   let context_root = base_dir // "context" in
-  State.read ~store_root ~context_root () >>= function
+  State.read
+    ~store_root ~context_root state_genesis_block >>= function
   | Error _ -> Pervasives.failwith "read err"
-  | Ok (state:State.global_state) ->
-      State.Chain.create state state_genesis_block
+  | Ok (_state, chain) ->
+      Lwt.return chain
 
 
 let block_header
diff --git a/src/lib_shell/test/test_state.ml b/src/lib_shell/test/test_state.ml
index 4acce23dd..0e36da8c0 100644
--- a/src/lib_shell/test/test_state.ml
+++ b/src/lib_shell/test/test_state.ml
@@ -127,7 +127,6 @@ type state = {
   vblock: (string, State.Block.t) Hashtbl.t ;
   state: State.t ;
   chain: State.Chain.t ;
-  init: unit -> State.t tzresult Lwt.t;
 }
 
 let vblock s = Hashtbl.find s.vblock
@@ -142,15 +141,12 @@ let wrap_state_init f base_dir =
   begin
     let store_root = base_dir // "store" in
     let context_root = base_dir // "context" in
-    let init () =
-      State.read
-        ~store_root
-        ~context_root
-        () in
-    init () >>=? fun state ->
-    State.Chain.create state genesis >>= fun chain ->
+    State.read
+      ~store_root
+      ~context_root
+      genesis >>=? fun (state, chain) ->
     build_example_tree chain >>= fun vblock ->
-    f { state ; chain ; vblock ; init } >>=? fun () ->
+    f { state ; chain ; vblock } >>=? fun () ->
     return ()
   end