diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
new file mode 100644
index 0000000..ed335ef
--- /dev/null
+++ b/.pre-commit-config.yaml
@@ -0,0 +1,2 @@
+ci: {}
+repos: []
diff --git a/src/api/add_snapshot.rs b/src/api/add_snapshot.rs
index d92174c..5ac42f5 100644
--- a/src/api/add_snapshot.rs
+++ b/src/api/add_snapshot.rs
@@ -98,7 +98,7 @@ mod test {
 
         let server = Server::new(Default::default(), storage);
         let app = App::new().configure(|sc| server.config(sc));
-        let mut app = test::init_service(app).await;
+        let app = test::init_service(app).await;
 
         let uri = format!("/v1/client/add-snapshot/{}", version_id);
         let req = test::TestRequest::post()
@@ -107,7 +107,7 @@ mod test {
             .insert_header((CLIENT_ID_HEADER, client_id.to_string()))
             .set_payload(b"abcd".to_vec())
             .to_request();
-        let resp = test::call_service(&mut app, req).await;
+        let resp = test::call_service(&app, req).await;
         assert_eq!(resp.status(), StatusCode::OK);
 
         // read back that snapshot
@@ -116,7 +116,7 @@ mod test {
             .uri(uri)
             .append_header((CLIENT_ID_HEADER, client_id.to_string()))
             .to_request();
-        let resp = test::call_service(&mut app, req).await;
+        let resp = test::call_service(&app, req).await;
         assert_eq!(resp.status(), StatusCode::OK);
 
         use actix_web::body::MessageBody;
@@ -140,7 +140,7 @@ mod test {
 
         let server = Server::new(Default::default(), storage);
         let app = App::new().configure(|sc| server.config(sc));
-        let mut app = test::init_service(app).await;
+        let app = test::init_service(app).await;
 
         // add a snapshot for a nonexistent version
         let uri = format!("/v1/client/add-snapshot/{}", version_id);
@@ -150,7 +150,7 @@ mod test {
             .append_header((CLIENT_ID_HEADER, client_id.to_string()))
             .set_payload(b"abcd".to_vec())
             .to_request();
-        let resp = test::call_service(&mut app, req).await;
+        let resp = test::call_service(&app, req).await;
         assert_eq!(resp.status(), StatusCode::OK);
 
         // read back, seeing no snapshot
@@ -159,7 +159,7 @@ mod test {
             .uri(uri)
             .append_header((CLIENT_ID_HEADER, client_id.to_string()))
             .to_request();
-        let resp = test::call_service(&mut app, req).await;
+        let resp = test::call_service(&app, req).await;
         assert_eq!(resp.status(), StatusCode::NOT_FOUND);
     }
 
@@ -170,7 +170,7 @@ mod test {
         let storage: Box<dyn Storage> = Box::new(InMemoryStorage::new());
         let server = Server::new(Default::default(), storage);
         let app = App::new().configure(|sc| server.config(sc));
-        let mut app = test::init_service(app).await;
+        let app = test::init_service(app).await;
 
         let uri = format!("/v1/client/add-snapshot/{}", version_id);
         let req = test::TestRequest::post()
@@ -179,7 +179,7 @@ mod test {
             .append_header((CLIENT_ID_HEADER, client_id.to_string()))
             .set_payload(b"abcd".to_vec())
             .to_request();
-        let resp = test::call_service(&mut app, req).await;
+        let resp = test::call_service(&app, req).await;
         assert_eq!(resp.status(), StatusCode::BAD_REQUEST);
     }
 
@@ -190,7 +190,7 @@ mod test {
         let storage: Box<dyn Storage> = Box::new(InMemoryStorage::new());
         let server = Server::new(Default::default(), storage);
         let app = App::new().configure(|sc| server.config(sc));
-        let mut app = test::init_service(app).await;
+        let app = test::init_service(app).await;
 
         let uri = format!("/v1/client/add-snapshot/{}", version_id);
         let req = test::TestRequest::post()
@@ -201,7 +201,7 @@ mod test {
             ))
             .append_header((CLIENT_ID_HEADER, client_id.to_string()))
             .to_request();
-        let resp = test::call_service(&mut app, req).await;
+        let resp = test::call_service(&app, req).await;
         assert_eq!(resp.status(), StatusCode::BAD_REQUEST);
     }
 }
diff --git a/src/api/add_version.rs b/src/api/add_version.rs
index 7428d94..d3d693b 100644
--- a/src/api/add_version.rs
+++ b/src/api/add_version.rs
@@ -126,7 +126,7 @@ mod test {
 
         let server = Server::new(Default::default(), storage);
         let app = App::new().configure(|sc| server.config(sc));
-        let mut app = test::init_service(app).await;
+        let app = test::init_service(app).await;
 
         let uri = format!("/v1/client/add-version/{}", parent_version_id);
         let req = test::TestRequest::post()
@@ -138,7 +138,7 @@ mod test {
             .append_header((CLIENT_ID_HEADER, client_id.to_string()))
             .set_payload(b"abcd".to_vec())
             .to_request();
-        let resp = test::call_service(&mut app, req).await;
+        let resp = test::call_service(&app, req).await;
         assert_eq!(resp.status(), StatusCode::OK);
 
         // the returned version ID is random, but let's check that it's not
@@ -168,7 +168,7 @@ mod test {
 
         let server = Server::new(Default::default(), storage);
         let app = App::new().configure(|sc| server.config(sc));
-        let mut app = test::init_service(app).await;
+        let app = test::init_service(app).await;
 
         let uri = format!("/v1/client/add-version/{}", parent_version_id);
         let req = test::TestRequest::post()
@@ -180,7 +180,7 @@ mod test {
             .append_header((CLIENT_ID_HEADER, client_id.to_string()))
             .set_payload(b"abcd".to_vec())
             .to_request();
-        let resp = test::call_service(&mut app, req).await;
+        let resp = test::call_service(&app, req).await;
         assert_eq!(resp.status(), StatusCode::CONFLICT);
         assert_eq!(resp.headers().get("X-Version-Id"), None);
         assert_eq!(
@@ -196,7 +196,7 @@ mod test {
         let storage: Box<dyn Storage> = Box::new(InMemoryStorage::new());
         let server = Server::new(Default::default(), storage);
         let app = App::new().configure(|sc| server.config(sc));
-        let mut app = test::init_service(app).await;
+        let app = test::init_service(app).await;
 
         let uri = format!("/v1/client/add-version/{}", parent_version_id);
         let req = test::TestRequest::post()
@@ -205,7 +205,7 @@ mod test {
             .append_header((CLIENT_ID_HEADER, client_id.to_string()))
             .set_payload(b"abcd".to_vec())
             .to_request();
-        let resp = test::call_service(&mut app, req).await;
+        let resp = test::call_service(&app, req).await;
         assert_eq!(resp.status(), StatusCode::BAD_REQUEST);
     }
 
@@ -216,7 +216,7 @@ mod test {
         let storage: Box<dyn Storage> = Box::new(InMemoryStorage::new());
         let server = Server::new(Default::default(), storage);
         let app = App::new().configure(|sc| server.config(sc));
-        let mut app = test::init_service(app).await;
+        let app = test::init_service(app).await;
 
         let uri = format!("/v1/client/add-version/{}", parent_version_id);
         let req = test::TestRequest::post()
@@ -227,7 +227,7 @@ mod test {
             ))
             .append_header((CLIENT_ID_HEADER, client_id.to_string()))
             .to_request();
-        let resp = test::call_service(&mut app, req).await;
+        let resp = test::call_service(&app, req).await;
         assert_eq!(resp.status(), StatusCode::BAD_REQUEST);
     }
 }
diff --git a/src/api/get_child_version.rs b/src/api/get_child_version.rs
index cb0e74f..2a1ffbf 100644
--- a/src/api/get_child_version.rs
+++ b/src/api/get_child_version.rs
@@ -81,14 +81,14 @@ mod test {
 
         let server = Server::new(Default::default(), storage);
         let app = App::new().configure(|sc| server.config(sc));
-        let mut app = test::init_service(app).await;
+        let app = test::init_service(app).await;
 
         let uri = format!("/v1/client/get-child-version/{}", parent_version_id);
         let req = test::TestRequest::get()
             .uri(&uri)
             .append_header((CLIENT_ID_HEADER, client_id.to_string()))
             .to_request();
-        let resp = test::call_service(&mut app, req).await;
+        let resp = test::call_service(&app, req).await;
         assert_eq!(resp.status(), StatusCode::OK);
         assert_eq!(
             resp.headers().get("X-Version-Id").unwrap(),
@@ -115,14 +115,14 @@ mod test {
         let storage: Box<dyn Storage> = Box::new(InMemoryStorage::new());
         let server = Server::new(Default::default(), storage);
         let app = App::new().configure(|sc| server.config(sc));
-        let mut app = test::init_service(app).await;
+        let app = test::init_service(app).await;
 
         let uri = format!("/v1/client/get-child-version/{}", parent_version_id);
         let req = test::TestRequest::get()
             .uri(&uri)
             .append_header((CLIENT_ID_HEADER, client_id.to_string()))
             .to_request();
-        let resp = test::call_service(&mut app, req).await;
+        let resp = test::call_service(&app, req).await;
         assert_eq!(resp.status(), StatusCode::NOT_FOUND);
         assert_eq!(resp.headers().get("X-Version-Id"), None);
         assert_eq!(resp.headers().get("X-Parent-Version-Id"), None);
@@ -141,7 +141,7 @@ mod test {
         }
         let server = Server::new(Default::default(), storage);
         let app = App::new().configure(|sc| server.config(sc));
-        let mut app = test::init_service(app).await;
+        let app = test::init_service(app).await;
 
         // the child of an unknown parent_version_id is GONE
         let uri = format!("/v1/client/get-child-version/{}", parent_version_id);
@@ -149,7 +149,7 @@ mod test {
             .uri(&uri)
             .append_header((CLIENT_ID_HEADER, client_id.to_string()))
             .to_request();
-        let resp = test::call_service(&mut app, req).await;
+        let resp = test::call_service(&app, req).await;
         assert_eq!(resp.status(), StatusCode::GONE);
         assert_eq!(resp.headers().get("X-Version-Id"), None);
         assert_eq!(resp.headers().get("X-Parent-Version-Id"), None);
@@ -162,7 +162,7 @@ mod test {
             .uri(&uri)
             .append_header((CLIENT_ID_HEADER, client_id.to_string()))
             .to_request();
-        let resp = test::call_service(&mut app, req).await;
+        let resp = test::call_service(&app, req).await;
         assert_eq!(resp.status(), StatusCode::NOT_FOUND);
         assert_eq!(resp.headers().get("X-Version-Id"), None);
         assert_eq!(resp.headers().get("X-Parent-Version-Id"), None);
diff --git a/src/api/get_snapshot.rs b/src/api/get_snapshot.rs
index 4135257..1776ef5 100644
--- a/src/api/get_snapshot.rs
+++ b/src/api/get_snapshot.rs
@@ -62,14 +62,14 @@ mod test {
 
         let server = Server::new(Default::default(), storage);
         let app = App::new().configure(|sc| server.config(sc));
-        let mut app = test::init_service(app).await;
+        let app = test::init_service(app).await;
 
         let uri = "/v1/client/snapshot";
         let req = test::TestRequest::get()
             .uri(uri)
             .append_header((CLIENT_ID_HEADER, client_id.to_string()))
             .to_request();
-        let resp = test::call_service(&mut app, req).await;
+        let resp = test::call_service(&app, req).await;
         assert_eq!(resp.status(), StatusCode::NOT_FOUND);
     }
 
@@ -98,14 +98,14 @@ mod test {
 
         let server = Server::new(Default::default(), storage);
         let app = App::new().configure(|sc| server.config(sc));
-        let mut app = test::init_service(app).await;
+        let app = test::init_service(app).await;
 
         let uri = "/v1/client/snapshot";
         let req = test::TestRequest::get()
             .uri(uri)
             .append_header((CLIENT_ID_HEADER, client_id.to_string()))
             .to_request();
-        let resp = test::call_service(&mut app, req).await;
+        let resp = test::call_service(&app, req).await;
         assert_eq!(resp.status(), StatusCode::OK);
 
         use actix_web::body::MessageBody;
diff --git a/src/bin/taskchampion-sync-server.rs b/src/bin/taskchampion-sync-server.rs
index 76401a6..e25ce2c 100644
--- a/src/bin/taskchampion-sync-server.rs
+++ b/src/bin/taskchampion-sync-server.rs
@@ -68,10 +68,10 @@ mod test {
     async fn test_index_get() {
         let server = Server::new(Default::default(), Box::new(InMemoryStorage::new()));
         let app = App::new().configure(|sc| server.config(sc));
-        let mut app = test::init_service(app).await;
+        let app = test::init_service(app).await;
 
         let req = test::TestRequest::get().uri("/").to_request();
-        let resp = test::call_service(&mut app, req).await;
+        let resp = test::call_service(&app, req).await;
         assert!(resp.status().is_success());
     }
 }
diff --git a/src/lib.rs b/src/lib.rs
index 5ba4658..a4d52bf 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -59,10 +59,10 @@ mod test {
     async fn test_cache_control() {
         let server = Server::new(Default::default(), Box::new(InMemoryStorage::new()));
         let app = App::new().configure(|sc| server.config(sc));
-        let mut app = test::init_service(app).await;
+        let app = test::init_service(app).await;
 
         let req = test::TestRequest::get().uri("/").to_request();
-        let resp = test::call_service(&mut app, req).await;
+        let resp = test::call_service(&app, req).await;
         assert!(resp.status().is_success());
         assert_eq!(
             resp.headers().get("Cache-Control").unwrap(),
diff --git a/src/storage/inmemory.rs b/src/storage/inmemory.rs
index 3b17720..fcb5ac6 100644
--- a/src/storage/inmemory.rs
+++ b/src/storage/inmemory.rs
@@ -47,7 +47,7 @@ impl<'a> StorageTxn for InnerTxn<'a> {
     }
 
     fn new_client(&mut self, client_id: Uuid, latest_version_id: Uuid) -> anyhow::Result<()> {
-        if self.0.clients.get(&client_id).is_some() {
+        if self.0.clients.contains_key(&client_id) {
             return Err(anyhow::anyhow!("Client {} already exists", client_id));
         }
         self.0.clients.insert(