diff --git a/Sources/SparkConnect/SparkConnectClient.swift b/Sources/SparkConnect/SparkConnectClient.swift
index a5306dc..5c6b4cc 100644
--- a/Sources/SparkConnect/SparkConnectClient.swift
+++ b/Sources/SparkConnect/SparkConnectClient.swift
@@ -82,8 +82,17 @@ public actor SparkConnectClient {
     self.userContext = userName.toUserContext
   }
 
-  /// Stop the connection. Currently, this API is no-op because we don't reuse the connection yet.
-  func stop() {
+  /// Stop the connection.
+  func stop() async {
+    guard self.sessionID != nil else { return }
+    try? await withGPRC { client in
+      let service = SparkConnectService.Client(wrapping: client)
+      var request = Spark_Connect_ReleaseSessionRequest()
+      request.sessionID = self.sessionID!
+      request.userContext = self.userContext
+      request.clientType = self.clientType
+      _ = try await service.releaseSession(request)
+    }
   }
 
   /// Connect to the `Spark Connect` server with the given session ID string.
diff --git a/Tests/SparkConnectTests/SparkSessionTests.swift b/Tests/SparkConnectTests/SparkSessionTests.swift
index e8213cc..7404395 100644
--- a/Tests/SparkConnectTests/SparkSessionTests.swift
+++ b/Tests/SparkConnectTests/SparkSessionTests.swift
@@ -27,6 +27,7 @@ import Testing
 struct SparkSessionTests {
   @Test
   func sparkContext() async throws {
+    await SparkSession.builder.clear()
     let spark = try await SparkSession.builder.getOrCreate()
     await #expect(throws: SparkConnectError.UnsupportedOperationException) {
       try await spark.sparkContext
@@ -36,12 +37,14 @@ struct SparkSessionTests {
 
   @Test
   func stop() async throws {
+    await SparkSession.builder.clear()
     let spark = try await SparkSession.builder.getOrCreate()
     await spark.stop()
   }
 
   @Test
   func newSession() async throws {
+    await SparkSession.builder.clear()
     let spark = try await SparkSession.builder.getOrCreate()
     await spark.stop()
     let newSpark = try await spark.newSession()
@@ -52,8 +55,8 @@ struct SparkSessionTests {
 
   @Test
   func sessionID() async throws {
+    await SparkSession.builder.clear()
     let spark1 = try await SparkSession.builder.getOrCreate()
-    await spark1.stop()
     let remote = ProcessInfo.processInfo.environment["SPARK_REMOTE"] ?? "sc://localhost"
     let spark2 = try await SparkSession.builder.remote("\(remote)/;session_id=\(spark1.sessionID)").getOrCreate()
     await spark2.stop()
@@ -61,7 +64,22 @@ struct SparkSessionTests {
     #expect(spark1 == spark2)
   }
 
+  @Test
+  func closedSessionID() async throws {
+    await SparkSession.builder.clear()
+    let spark1 = try await SparkSession.builder.getOrCreate()
+    if await spark1.version >= "4.0.0" {
+      let sessionID = spark1.sessionID
+      await spark1.stop()
+      let remote = ProcessInfo.processInfo.environment["SPARK_REMOTE"] ?? "sc://localhost"
+      try await #require(throws: Error.self) {
+        try await SparkSession.builder.remote("\(remote)/;session_id=\(sessionID)").getOrCreate()
+      }
+    }
+  }
+
   @Test func userContext() async throws {
+    await SparkSession.builder.clear()
     let spark = try await SparkSession.builder.getOrCreate()
 #if os(macOS) || os(Linux)
     let defaultUserContext = ProcessInfo.processInfo.userName.toUserContext
@@ -74,6 +92,7 @@ struct SparkSessionTests {
 
   @Test
   func version() async throws {
+    await SparkSession.builder.clear()
     let spark = try await SparkSession.builder.getOrCreate()
     let version = await spark.version
     #expect(version.starts(with: "4.0.0") || version.starts(with: "3.5."))
@@ -82,6 +101,7 @@ struct SparkSessionTests {
 
   @Test
   func conf() async throws {
+    await SparkSession.builder.clear()
     let spark = try await SparkSession.builder.getOrCreate()
     try await spark.conf.set("spark.x", "y")
     #expect(try await spark.conf.get("spark.x") == "y")
@@ -91,6 +111,7 @@ struct SparkSessionTests {
 
   @Test
   func emptyDataFrame() async throws {
+    await SparkSession.builder.clear()
     let spark = try await SparkSession.builder.getOrCreate()
     #expect(try await spark.emptyDataFrame.count() == 0)
     #expect(try await spark.emptyDataFrame.dtypes.isEmpty)
@@ -100,6 +121,7 @@ struct SparkSessionTests {
 
   @Test
   func range() async throws {
+    await SparkSession.builder.clear()
     let spark = try await SparkSession.builder.getOrCreate()
     #expect(try await spark.range(10).count() == 10)
     #expect(try await spark.range(0, 100).count() == 100)
@@ -110,6 +132,7 @@ struct SparkSessionTests {
 #if !os(Linux)
   @Test
   func sql() async throws {
+    await SparkSession.builder.clear()
     let spark = try await SparkSession.builder.getOrCreate()
     let expected = [Row(true, 1, "a")]
     if await spark.version.starts(with: "4.") {
@@ -122,6 +145,7 @@ struct SparkSessionTests {
 
   @Test
   func table() async throws {
+    await SparkSession.builder.clear()
     let tableName = "TABLE_" + UUID().uuidString.replacingOccurrences(of: "-", with: "")
     let spark = try await SparkSession.builder.getOrCreate()
     try await SQLHelper.withTable(spark, tableName)({
@@ -133,6 +157,7 @@ struct SparkSessionTests {
 
   @Test
   func time() async throws {
+    await SparkSession.builder.clear()
     let spark = try await SparkSession.builder.getOrCreate()
     #expect(try await spark.time(spark.range(1000).count) == 1000)
 #if !os(Linux)
@@ -144,6 +169,7 @@ struct SparkSessionTests {
 
   @Test
   func tag() async throws {
+    await SparkSession.builder.clear()
     let spark = try await SparkSession.builder.getOrCreate()
     try await spark.addTag("tag1")
     #expect(await spark.getTags() == Set(["tag1"]))
@@ -158,6 +184,7 @@ struct SparkSessionTests {
 
   @Test
   func invalidTags() async throws {
+    await SparkSession.builder.clear()
     let spark = try await SparkSession.builder.getOrCreate()
     await #expect(throws: SparkConnectError.InvalidArgumentException) {
       try await spark.addTag("")
@@ -170,6 +197,7 @@ struct SparkSessionTests {
 
   @Test
   func interruptAll() async throws {
+    await SparkSession.builder.clear()
     let spark = try await SparkSession.builder.getOrCreate()
     #expect(try await spark.interruptAll() == [])
     await spark.stop()
@@ -177,6 +205,7 @@ struct SparkSessionTests {
 
   @Test
   func interruptTag() async throws {
+    await SparkSession.builder.clear()
     let spark = try await SparkSession.builder.getOrCreate()
     #expect(try await spark.interruptTag("etl") == [])
     await spark.stop()
@@ -184,6 +213,7 @@ struct SparkSessionTests {
 
   @Test
   func interruptOperation() async throws {
+    await SparkSession.builder.clear()
     let spark = try await SparkSession.builder.getOrCreate()
     #expect(try await spark.interruptOperation("id") == [])
     await spark.stop()