diff --git a/Cargo.lock b/Cargo.lock
index c4c09ef..dcb0a1e 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -2,18 +2,162 @@
 # It is not intended for manual editing.
 version = 3
 
+[[package]]
+name = "aho-corasick"
+version = "1.1.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8e60d3430d3a69478ad0993f19238d2df97c507009a52b3c10addcd7f6bcb916"
+dependencies = [
+ "memchr",
+]
+
 [[package]]
 name = "autocfg"
 version = "1.3.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "0c4b4d0bd25bd0b74681c0ad21497610ce1b7c91b1022cd21c80c6fbdd9476b0"
 
+[[package]]
+name = "cfg-if"
+version = "1.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "baf1de4339761588bc0619e3cbc0120ee582ebb74b53b4efbf79117bd2da40fd"
+
 [[package]]
 name = "either"
 version = "1.13.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "60b1af1c220855b6ceac025d3f6ecdd2b7c4894bfe9cd9bda4fbb4bc7c0d4cf0"
 
+[[package]]
+name = "equivalent"
+version = "1.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5443807d6dff69373d433ab9ef5378ad8df50ca6298caf15de6e52e24aaf54d5"
+
+[[package]]
+name = "futures"
+version = "0.3.30"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "645c6916888f6cb6350d2550b80fb63e734897a8498abe35cfb732b6487804b0"
+dependencies = [
+ "futures-channel",
+ "futures-core",
+ "futures-executor",
+ "futures-io",
+ "futures-sink",
+ "futures-task",
+ "futures-util",
+]
+
+[[package]]
+name = "futures-channel"
+version = "0.3.30"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "eac8f7d7865dcb88bd4373ab671c8cf4508703796caa2b1985a9ca867b3fcb78"
+dependencies = [
+ "futures-core",
+ "futures-sink",
+]
+
+[[package]]
+name = "futures-core"
+version = "0.3.30"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "dfc6580bb841c5a68e9ef15c77ccc837b40a7504914d52e47b8b0e9bbda25a1d"
+
+[[package]]
+name = "futures-executor"
+version = "0.3.30"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a576fc72ae164fca6b9db127eaa9a9dda0d61316034f33a0a0d4eda41f02b01d"
+dependencies = [
+ "futures-core",
+ "futures-task",
+ "futures-util",
+]
+
+[[package]]
+name = "futures-io"
+version = "0.3.30"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a44623e20b9681a318efdd71c299b6b222ed6f231972bfe2f224ebad6311f0c1"
+
+[[package]]
+name = "futures-macro"
+version = "0.3.30"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "87750cf4b7a4c0625b1529e4c543c2182106e4dedc60a2a6455e00d212c489ac"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
+[[package]]
+name = "futures-sink"
+version = "0.3.30"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9fb8e00e87438d937621c1c6269e53f536c14d3fbd6a042bb24879e57d474fb5"
+
+[[package]]
+name = "futures-task"
+version = "0.3.30"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "38d84fa142264698cdce1a9f9172cf383a0c82de1bddcf3092901442c4097004"
+
+[[package]]
+name = "futures-timer"
+version = "3.0.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f288b0a4f20f9a56b5d1da57e2227c661b7b16168e2f72365f57b63326e29b24"
+
+[[package]]
+name = "futures-util"
+version = "0.3.30"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3d6401deb83407ab3da39eba7e33987a73c3df0c82b4bb5813ee871c19c41d48"
+dependencies = [
+ "futures-channel",
+ "futures-core",
+ "futures-io",
+ "futures-macro",
+ "futures-sink",
+ "futures-task",
+ "memchr",
+ "pin-project-lite",
+ "pin-utils",
+ "slab",
+]
+
+[[package]]
+name = "glob"
+version = "0.3.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d2fabcfbdc87f4758337ca535fb41a6d701b65693ce38287d856d1674551ec9b"
+
+[[package]]
+name = "hashbrown"
+version = "0.14.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e5274423e17b7c9fc20b6e7e208532f9b19825d82dfd615708b70edd83df41f1"
+
+[[package]]
+name = "indexmap"
+version = "2.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "93ead53efc7ea8ed3cfb0c79fc8023fbb782a5432b52830b6518941cebe6505c"
+dependencies = [
+ "equivalent",
+ "hashbrown",
+]
+
+[[package]]
+name = "memchr"
+version = "2.7.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "78ca9ab1a0babb1e7d5695e3530886289c18cf2f87ec19a575a0abdce112e3a3"
+
 [[package]]
 name = "num-traits"
 version = "0.2.19"
@@ -29,6 +173,7 @@ version = "0.2.0"
 dependencies = [
  "either",
  "ordered-float",
+ "rstest",
  "rustc-hash",
 ]
 
@@ -41,8 +186,179 @@ dependencies = [
  "num-traits",
 ]
 
+[[package]]
+name = "pin-project-lite"
+version = "0.2.14"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bda66fc9667c18cb2758a2ac84d1167245054bcf85d5d1aaa6923f45801bdd02"
+
+[[package]]
+name = "pin-utils"
+version = "0.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8b870d8c151b6f2fb93e84a13146138f05d02ed11c7e7c54f8826aaaf7c9f184"
+
+[[package]]
+name = "proc-macro-crate"
+version = "3.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6d37c51ca738a55da99dc0c4a34860fd675453b8b36209178c2249bb13651284"
+dependencies = [
+ "toml_edit",
+]
+
+[[package]]
+name = "proc-macro2"
+version = "1.0.86"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5e719e8df665df0d1c8fbfd238015744736151d4445ec0836b8e628aae103b77"
+dependencies = [
+ "unicode-ident",
+]
+
+[[package]]
+name = "quote"
+version = "1.0.36"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0fa76aaf39101c457836aec0ce2316dbdc3ab723cdda1c6bd4e6ad4208acaca7"
+dependencies = [
+ "proc-macro2",
+]
+
+[[package]]
+name = "regex"
+version = "1.10.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4219d74c6b67a3654a9fbebc4b419e22126d13d2f3c4a07ee0cb61ff79a79619"
+dependencies = [
+ "aho-corasick",
+ "memchr",
+ "regex-automata",
+ "regex-syntax",
+]
+
+[[package]]
+name = "regex-automata"
+version = "0.4.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "38caf58cc5ef2fed281f89292ef23f6365465ed9a41b7a7754eb4e26496c92df"
+dependencies = [
+ "aho-corasick",
+ "memchr",
+ "regex-syntax",
+]
+
+[[package]]
+name = "regex-syntax"
+version = "0.8.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7a66a03ae7c801facd77a29370b4faec201768915ac14a721ba36f20bc9c209b"
+
+[[package]]
+name = "relative-path"
+version = "1.9.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ba39f3699c378cd8970968dcbff9c43159ea4cfbd88d43c00b22f2ef10a435d2"
+
+[[package]]
+name = "rstest"
+version = "0.22.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7b423f0e62bdd61734b67cd21ff50871dfaeb9cc74f869dcd6af974fbcb19936"
+dependencies = [
+ "futures",
+ "futures-timer",
+ "rstest_macros",
+ "rustc_version",
+]
+
+[[package]]
+name = "rstest_macros"
+version = "0.22.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c5e1711e7d14f74b12a58411c542185ef7fb7f2e7f8ee6e2940a883628522b42"
+dependencies = [
+ "cfg-if",
+ "glob",
+ "proc-macro-crate",
+ "proc-macro2",
+ "quote",
+ "regex",
+ "relative-path",
+ "rustc_version",
+ "syn",
+ "unicode-ident",
+]
+
 [[package]]
 name = "rustc-hash"
 version = "2.0.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "583034fd73374156e66797ed8e5b0d5690409c9226b22d87cb7f19821c05d152"
+
+[[package]]
+name = "rustc_version"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bfa0f585226d2e68097d4f95d113b15b83a82e819ab25717ec0590d9584ef366"
+dependencies = [
+ "semver",
+]
+
+[[package]]
+name = "semver"
+version = "1.0.23"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "61697e0a1c7e512e84a621326239844a24d8207b4669b41bc18b32ea5cbf988b"
+
+[[package]]
+name = "slab"
+version = "0.4.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8f92a496fb766b417c996b9c5e57daf2f7ad3b0bebe1ccfca4856390e3d3bb67"
+dependencies = [
+ "autocfg",
+]
+
+[[package]]
+name = "syn"
+version = "2.0.74"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1fceb41e3d546d0bd83421d3409b1460cc7444cd389341a4c880fe7a042cb3d7"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "unicode-ident",
+]
+
+[[package]]
+name = "toml_datetime"
+version = "0.6.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0dd7358ecb8fc2f8d014bf86f6f638ce72ba252a2c3a2572f2a795f1d23efb41"
+
+[[package]]
+name = "toml_edit"
+version = "0.21.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6a8534fd7f78b5405e860340ad6575217ce99f38d4d5c8f2442cb5ecb50090e1"
+dependencies = [
+ "indexmap",
+ "toml_datetime",
+ "winnow",
+]
+
+[[package]]
+name = "unicode-ident"
+version = "1.0.12"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3354b9ac3fae1ff6755cb6db53683adb661634f67557942dea4facebec0fee4b"
+
+[[package]]
+name = "winnow"
+version = "0.5.40"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f593a95398737aeed53e489c785df13f3618e41dbcd6718c6addbf1395aa6876"
+dependencies = [
+ "memchr",
+]
diff --git a/Cargo.toml b/Cargo.toml
index eb560d5..28e337e 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -9,3 +9,6 @@ rust-version = "1.70"
 either = "1.13.0"
 ordered-float = "4.2.2"
 rustc-hash = "2.0.0"
+
+[dev-dependencies]
+rstest = "0.22.0"
diff --git a/src/book.rs b/src/book.rs
index a8a9abb..0667c8f 100644
--- a/src/book.rs
+++ b/src/book.rs
@@ -25,11 +25,11 @@ pub struct Client {
 }
 
 impl Client {
-    pub fn new() -> Client {
+    pub fn new() -> Rc<Client> {
         CLIENT_ID.with(|thread_id| {
             let id = thread_id.get();
             thread_id.set(id + 1);
-            Self { id }
+            Rc::new(Self { id })
         })
     }
 }
@@ -354,15 +354,134 @@ fn is_deeper(a: f64, b: f64, side: &Side) -> bool {
 #[cfg(test)]
 mod test {
     use super::*;
+    use rstest::*;
 
-    #[test]
-    fn test_empty_order_book() {
-        let ob = OrderBook::new();
-        assert!(ob.get_ladder(&Side::Bid).is_empty());
-        assert!(ob.get_ladder(&Side::Ask).is_empty());
+    #[fixture]
+    fn ob() -> OrderBook {
+        OrderBook::new()
+    }
+
+    #[rstest]
+    #[case(Side::Bid)]
+    #[case(Side::Ask)]
+    fn test_empty_order_book(#[by_ref] ob: &OrderBook, #[case] side: Side) {
+        assert!(ob.get_ladder(&side).is_empty());
+    }
+
+    #[rstest]
+    fn test_empty_bid(#[by_ref] ob: &OrderBook) {
         assert_eq!(ob.best_bid(), None);
         assert_eq!(ob.best_bid_size(), None);
+    }
+
+    #[rstest]
+    fn test_empty_ask(#[by_ref] ob: &OrderBook) {
         assert_eq!(ob.best_ask(), None);
         assert_eq!(ob.best_ask_size(), None);
     }
+
+    #[test]
+    fn test_client_id() {
+        let client1 = Client::new();
+        let client2 = Client::new();
+        assert_ne!(client1.id, client2.id);
+    }
+
+    #[fixture]
+    fn client() -> Rc<Client> {
+        Client::new()
+    }
+
+    #[rstest]
+    #[case(-1.0, 0)]
+    #[case(-1.0, 1)]
+    #[case(0.0, 1)]
+    fn test_invalid_order(
+        #[by_ref] ob: &OrderBook,
+        client: Rc<Client>,
+        #[case] price: f64,
+        #[case] size: u64,
+    ) {
+        let order = Order::new(Side::Bid, price, size, &client);
+        assert!(ob.validate_order(&order).is_err());
+    }
+
+    #[fixture]
+    fn order(client: Rc<Client>) -> Order {
+        Order::new(Side::Bid, 1.0, 1, &client)
+    }
+
+    #[rstest]
+    fn test_valid_order(#[by_ref] ob: &OrderBook, #[by_ref] order: &Order) {
+        assert!(ob.validate_order(&order).is_ok());
+    }
+
+    #[rstest]
+    fn test_passive_placement(mut ob: OrderBook, order: Order) {
+        let result = ob.insert(order);
+        assert!(matches!(result, OrderBookResult::OrderId(_)));
+    }
+
+    #[rstest]
+    fn test_cancel_order(mut ob: OrderBook, order: Order) {
+        let order_id = match ob.insert(order) {
+            OrderBookResult::OrderId(id) => id,
+            _ => unreachable!(),
+        };
+        let result = ob.cancel(order_id);
+        assert!(matches!(result, OrderBookResult::Canceled));
+    }
+
+    #[rstest]
+    fn test_cancel_invalid_order(mut ob: OrderBook, order: Order) {
+        ob.insert(order);
+        let result = ob.cancel(18378);
+        assert!(matches!(result, OrderBookResult::Error(_)));
+    }
+
+    #[rstest]
+    fn test_best_bid(mut ob: OrderBook, client: Rc<Client>) {
+        let prices = vec![1.4, 1.5, 1.6, 1.3, 1.8, 1.4];
+        let sizes = vec![1, 2, 3, 4, 5, 6];
+
+        for (price, size) in prices.iter().zip(sizes.iter()) {
+            let order = Order::new(Side::Bid, *price, *size, &client);
+            ob.insert(order);
+        }
+
+        assert_eq!(ob.best_bid(), Some(1.8));
+        assert_eq!(ob.best_bid_size(), Some(5));
+    }
+
+    #[rstest]
+    fn test_best_ask(mut ob: OrderBook, client: Rc<Client>) {
+        let prices = vec![1.4, 1.5, 1.6, 1.3, 1.8, 1.4];
+        let sizes = vec![1, 2, 3, 4, 5, 6];
+
+        for (price, size) in prices.iter().zip(sizes.iter()) {
+            let order = Order::new(Side::Ask, *price, *size, &client);
+            ob.insert(order);
+        }
+
+        assert_eq!(ob.best_ask(), Some(1.3));
+        assert_eq!(ob.best_ask_size(), Some(4));
+    }
+
+    #[rstest]
+    fn test_partial_fill(mut ob: OrderBook, client: Rc<Client>) {
+        let order1 = Order::new(Side::Bid, 1.5, 1, &client);
+        let order2 = Order::new(Side::Ask, 1.5, 2, &client);
+        ob.insert(order1);
+
+        if let OrderBookResult::OrderIdTrades(_, trades) = ob.insert(order2) {
+            let trade = &trades[0];
+            assert_eq!(trade.price, 1.5);
+            assert_eq!(trade.size, 1);
+            assert_eq!(trades.len(), 1);
+        } else {
+            unreachable!();
+        }
+
+        assert_eq!(ob.best_ask_size(), Some(1));
+    }
 }
diff --git a/src/main.rs b/src/main.rs
index d01dad6..cd5b92c 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,10 +1,9 @@
 use orderbook::book::{Client, Order, OrderBook, OrderBookResult, Side};
-use std::rc::Rc;
 
 fn main() {
     let mut ob = OrderBook::new();
-    let client1 = Rc::new(Client::new());
-    let client2 = Rc::new(Client::new());
+    let client1 = Client::new();
+    let client2 = Client::new();
 
     // Initial order book
     {