diff --git a/openraft/src/error.rs b/openraft/src/error.rs
index d61c155fa..892dde14b 100644
--- a/openraft/src/error.rs
+++ b/openraft/src/error.rs
@@ -9,7 +9,6 @@ use serde::Serialize;
 
 use crate::raft_types::SnapshotSegmentId;
 use crate::LogId;
-use crate::Membership;
 use crate::NodeId;
 use crate::StorageError;
 
@@ -117,12 +116,6 @@ pub enum ChangeMembershipError {
         matched: Option<LogId>,
         distance: u64,
     },
-
-    // TODO(xp): test it in unittest
-    // TODO(xp): rename this error to some elaborated name.
-    // TODO(xp): 111 test it
-    #[error("now allowed to change from {curr:?} to {to:?}")]
-    Incompatible { curr: Membership, to: BTreeSet<NodeId> },
 }
 
 #[derive(Debug, thiserror::Error)]
diff --git a/openraft/src/lib.rs b/openraft/src/lib.rs
index e246293eb..ba9eb532b 100644
--- a/openraft/src/lib.rs
+++ b/openraft/src/lib.rs
@@ -7,7 +7,6 @@ mod defensive;
 mod membership;
 mod raft_types;
 mod replication;
-pub mod storage;
 mod storage_error;
 mod store_ext;
 mod store_wrapper;
@@ -17,6 +16,7 @@ pub mod error;
 pub mod metrics;
 pub mod network;
 pub mod raft;
+pub mod storage;
 pub mod testing;
 
 #[cfg(test)]
@@ -32,10 +32,6 @@ pub use crate::config::SnapshotPolicy;
 pub use crate::core::EffectiveMembership;
 pub use crate::core::State;
 pub use crate::defensive::DefensiveCheck;
-pub use crate::error::ChangeMembershipError;
-pub use crate::error::ClientWriteError;
-pub use crate::error::InitializeError;
-pub use crate::error::ReplicationError;
 pub use crate::membership::Membership;
 pub use crate::metrics::RaftMetrics;
 pub use crate::network::RaftNetwork;
diff --git a/openraft/src/replication/mod.rs b/openraft/src/replication/mod.rs
index dd667e927..2a75e4954 100644
--- a/openraft/src/replication/mod.rs
+++ b/openraft/src/replication/mod.rs
@@ -22,6 +22,7 @@ use tracing::Span;
 use crate::config::Config;
 use crate::config::SnapshotPolicy;
 use crate::error::LackEntry;
+use crate::error::ReplicationError;
 use crate::raft::AppendEntriesRequest;
 use crate::raft::InstallSnapshotRequest;
 use crate::raft_types::LogIdOptionExt;
@@ -34,7 +35,6 @@ use crate::MessageSummary;
 use crate::NodeId;
 use crate::RaftNetwork;
 use crate::RaftStorage;
-use crate::ReplicationError;
 
 #[derive(Default, Debug, Clone, Serialize, Deserialize, PartialEq, Eq)]
 pub struct ReplicationMetrics {
diff --git a/openraft/tests/membership/t20_change_membership.rs b/openraft/tests/membership/t20_change_membership.rs
index 7a07ee821..7a36a9164 100644
--- a/openraft/tests/membership/t20_change_membership.rs
+++ b/openraft/tests/membership/t20_change_membership.rs
@@ -3,7 +3,7 @@ use std::sync::Arc;
 use std::time::Duration;
 
 use maplit::btreeset;
-use openraft::ChangeMembershipError;
+use openraft::error::ChangeMembershipError;
 use openraft::Config;
 use openraft::RaftStorage;
 
diff --git a/rust-toolchain b/rust-toolchain
index 182ac38d2..a8a615915 100644
--- a/rust-toolchain
+++ b/rust-toolchain
@@ -1 +1 @@
-nightly-2022-01-03
+nightly-2022-01-01
diff --git a/rust-toolchain.toml b/rust-toolchain.toml
new file mode 100644
index 000000000..c1b210927
--- /dev/null
+++ b/rust-toolchain.toml
@@ -0,0 +1,3 @@
+[toolchain]
+channel = "nightly-2022-01-01"
+components = ["rustfmt", "clippy"]