diff -r 4cea6e50175b -r ec92b4ed23aa test/test_tree.c
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/test/test_tree.c	Sun Sep 26 14:45:51 2021 +0200
@@ -0,0 +1,114 @@
+/*
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
+ *
+ * Copyright 2021 Mike Becker, Olaf Wintermann All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ *   1. Redistributions of source code must retain the above copyright
+ *      notice, this list of conditions and the following disclaimer.
+ *
+ *   2. Redistributions in binary form must reproduce the above copyright
+ *      notice, this list of conditions and the following disclaimer in the
+ *      documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "cx/tree.h"
+#include "test_config.h"
+
+#include <stddef.h>
+
+typedef struct TestNode TestNode;
+
+struct TestNode {
+    TestNode *parent;
+    TestNode *prev;
+    TestNode *next;
+    
+    TestNode *children_begin;
+    TestNode *children_end;
+    
+    int content;
+};
+
+void test_cx_tree_add_node() {
+    // prepare test tree
+    TestNode root;
+    memset(&root, 0, sizeof(TestNode));
+    
+    TestNode a;
+    memset(&a, 0, sizeof(TestNode));
+    root.children_begin = &a;
+    root.children_end = &a;
+    a.parent = &root;
+    a.content = 1;
+    
+    // new test nodes
+    TestNode b;
+    memset(&b, 0, sizeof(TestNode));
+    TestNode c;
+    memset(&c, 0, sizeof(TestNode));
+    
+    // test
+    b.content = 2;
+    int ret = cx_tree_add_node(&a, offsetof(TestNode, parent), offsetof(TestNode, prev), offsetof(TestNode, next), &b);
+    CU_ASSERT_EQUAL(ret, 0);
+    CU_ASSERT_PTR_EQUAL(b.parent, &root);
+    CU_ASSERT_PTR_EQUAL(b.prev, &a);
+    CU_ASSERT_PTR_EQUAL(b.next, NULL);
+    CU_ASSERT_PTR_EQUAL(a.next, &b);
+    
+    c.content = 3;
+    ret = cx_tree_add_node(&a, -1, -1, offsetof(TestNode, next), &c);
+    CU_ASSERT_EQUAL(ret, 0);
+    CU_ASSERT_PTR_EQUAL(c.parent, NULL);
+    CU_ASSERT_PTR_EQUAL(c.prev, NULL);
+    CU_ASSERT_PTR_EQUAL(c.next, NULL);
+    CU_ASSERT_PTR_EQUAL(b.next, &c);
+}
+
+int main() {
+    CU_pSuite suite = NULL;
+
+    if (CUE_SUCCESS != CU_initialize_registry()) {
+        return CU_get_error();
+    }
+
+    suite = CU_add_suite("tree suite", NULL, NULL);
+    if (NULL == suite) {
+        CU_cleanup_registry();
+        return CU_get_error();
+    }
+
+    if (
+            !CU_add_test(suite, "ll add tree node", test_cx_tree_add_node)
+            ) {
+        CU_cleanup_registry();
+        return CU_get_error();
+    }
+    
+    
+    CU_basic_set_mode(UCX_CU_BRM);
+
+    int exitcode;
+    if (CU_basic_run_tests()) {
+        exitcode = CU_get_error();
+    } else {
+        exitcode = CU_get_number_of_failures() == 0 ? 0 : 1;
+    }
+    CU_cleanup_registry();
+    return exitcode;
+}