diff --git a/infra/common/src/main/java/cn/hippo4j/common/toolkit/JoinerTest.java b/infra/common/src/main/java/cn/hippo4j/common/toolkit/JoinerTest.java
new file mode 100644
index 0000000000..e8df954a07
--- /dev/null
+++ b/infra/common/src/main/java/cn/hippo4j/common/toolkit/JoinerTest.java
@@ -0,0 +1,92 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package cn.hippo4j.common.toolkit;
+
+import org.junit.Assert;
+import org.junit.Before;
+import org.junit.Test;
+import java.io.IOException;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.Iterator;
+
+public class JoinerTest {
+
+    private Joiner joiner;
+
+    @Before
+    public void init() {
+        joiner = Joiner.on(",");
+    }
+
+    @Test
+    public void testJoinWithSeparator() {
+        Assert.assertEquals("a,b,c", joiner.join(Arrays.asList("a", "b", "c")));
+        Assert.assertEquals("1,2,3", joiner.join(Arrays.asList(1, 2, 3)));
+        Assert.assertEquals("true,false,true", joiner.join(Arrays.asList(true, false, true)));
+    }
+
+    @Test
+    public void testJoinWithEmptyIterable() {
+        Assert.assertEquals("", joiner.join(Collections.emptyList()));
+    }
+
+    @Test
+    public void testJoinWithSingleElement() {
+        Assert.assertEquals("a", joiner.join(Collections.singletonList("a")));
+        Assert.assertEquals("1", joiner.join(Collections.singletonList(1)));
+        Assert.assertEquals("true", joiner.join(Collections.singletonList(true)));
+    }
+
+    @Test
+    public void testJoinWithCustomObject() {
+        Person person1 = new Person("Alice", 18);
+        Person person2 = new Person("Bob", 20);
+        Assert.assertEquals("Alice(18),Bob(20)", Joiner.on(",").join(Arrays.asList(person1, person2)));
+    }
+
+    private static class Person {
+        private String name;
+        private int age;
+
+        public Person(String name, int age) {
+            this.name = name;
+            this.age = age;
+        }
+
+        @Override
+        public String toString() {
+            return name + "(" + age + ")";
+        }
+    }
+
+    @Test(expected = NullPointerException.class)
+    public void testJoinWithNullIterator() {
+        Joiner.on(", ").join((Iterator<?>) null);
+    }
+
+    @Test(expected = NullPointerException.class)
+    public void testAppendToWithNullStringBuilder() throws IOException {
+        Joiner.on(", ").appendTo(null, Arrays.asList("a", "b").iterator());
+    }
+
+    @Test(expected = NullPointerException.class)
+    public void testAppendToWithNullAppendable() throws IOException {
+        Joiner.on(", ").appendTo(null, Arrays.asList("a", "b").iterator());
+    }
+}