diff -r 37c5d2fdb36b -r 68ad5750ba6b test/test_tree.c
--- a/test/test_tree.c	Tue Sep 28 18:49:12 2021 +0200
+++ b/test/test_tree.c	Sun Oct 03 10:43:31 2021 +0200
@@ -40,11 +40,9 @@
     
     TestNode *children_begin;
     TestNode *children_end;
-    
-    int content;
 };
 
-void test_cx_tree_add_node() {
+void test_cx_tree_add_node(void) {
     // prepare test tree
     TestNode root;
     memset(&root, 0, sizeof(TestNode));
@@ -54,8 +52,7 @@
     root.children_begin = &a;
     root.children_end = &a;
     a.parent = &root;
-    a.content = 1;
-    
+
     // new test nodes
     TestNode b;
     memset(&b, 0, sizeof(TestNode));
@@ -63,24 +60,22 @@
     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);
+    CU_ASSERT_EQUAL(ret, 0)
+    CU_ASSERT_PTR_EQUAL(b.parent, &root)
+    CU_ASSERT_PTR_EQUAL(b.prev, &a)
+    CU_ASSERT_PTR_NULL(b.next)
+    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);
+    CU_ASSERT_EQUAL(ret, 0)
+    CU_ASSERT_PTR_NULL(c.parent)
+    CU_ASSERT_PTR_NULL(c.prev)
+    CU_ASSERT_PTR_NULL(c.next)
+    CU_ASSERT_PTR_EQUAL(b.next, &c)
 }
 
-void test_cx_tree_add_child_node() {
+void test_cx_tree_add_child_node(void) {
     // prepare test tree
     TestNode root;
     memset(&root, 0, sizeof(TestNode));
@@ -97,7 +92,6 @@
     int ret;
     
     // test
-    a.content = 1;
     ret = cx_tree_add_child_node(
             &root,
             offsetof(TestNode, parent),
@@ -106,14 +100,13 @@
             (void**)&root.children_begin,
             (void**)&root.children_end,
             &a);
-    CU_ASSERT_EQUAL(ret, 0);
-    CU_ASSERT_PTR_EQUAL(root.children_begin, &a);
-    CU_ASSERT_PTR_EQUAL(root.children_end, &a);
-    CU_ASSERT_PTR_EQUAL(a.parent, &root);
-    CU_ASSERT_PTR_EQUAL(a.prev, NULL);
-    CU_ASSERT_PTR_EQUAL(a.next, NULL);
-    
-    b.content = 2;
+    CU_ASSERT_EQUAL(ret, 0)
+    CU_ASSERT_PTR_EQUAL(root.children_begin, &a)
+    CU_ASSERT_PTR_EQUAL(root.children_end, &a)
+    CU_ASSERT_PTR_EQUAL(a.parent, &root)
+    CU_ASSERT_PTR_NULL(a.prev)
+    CU_ASSERT_PTR_NULL(a.next)
+
     ret = cx_tree_add_child_node(
             &root,
             offsetof(TestNode, parent),
@@ -122,13 +115,13 @@
             (void**)&root.children_begin,
             (void**)&root.children_end,
             &b);
-    CU_ASSERT_EQUAL(ret, 0);
-    CU_ASSERT_TRUE(root.children_begin ? root.children_begin->next == &b : 0);
-    CU_ASSERT_PTR_EQUAL(root.children_end, &b);
-    CU_ASSERT_PTR_EQUAL(b.parent, &root);
-    CU_ASSERT_PTR_EQUAL(b.prev, &a);
+    CU_ASSERT_EQUAL(ret, 0)
+    CU_ASSERT_PTR_NOT_NULL(root.children_begin)
+    CU_ASSERT_PTR_EQUAL(root.children_begin->next, &b)
+    CU_ASSERT_PTR_EQUAL(root.children_end, &b)
+    CU_ASSERT_PTR_EQUAL(b.parent, &root)
+    CU_ASSERT_PTR_EQUAL(b.prev, &a)
     
-    c.content = 3;
     ret = cx_tree_add_child_node(
             &root,
             -1,
@@ -137,14 +130,13 @@
             (void**)&root.children_begin,
             NULL,
             &c);
-    CU_ASSERT_EQUAL(ret, 0);
-    CU_ASSERT_PTR_EQUAL(root.children_end, &b); // children_end unchanged
-    CU_ASSERT_PTR_EQUAL(b.next, &c);
-    CU_ASSERT_PTR_EQUAL(c.prev, NULL);
-    CU_ASSERT_PTR_EQUAL(c.next, NULL);
-    CU_ASSERT_PTR_EQUAL(c.parent, NULL);
+    CU_ASSERT_EQUAL(ret, 0)
+    CU_ASSERT_PTR_EQUAL(root.children_end, &b) // children_end unchanged
+    CU_ASSERT_PTR_EQUAL(b.next, &c)
+    CU_ASSERT_PTR_NULL(c.prev)
+    CU_ASSERT_PTR_NULL(c.next)
+    CU_ASSERT_PTR_NULL(c.parent)
     
-    a1.content = 11;
     ret = cx_tree_add_child_node(
             &a,
             offsetof(TestNode, parent),
@@ -156,7 +148,8 @@
     CU_ASSERT_EQUAL(ret, 0);
     CU_ASSERT_PTR_EQUAL(a.children_begin, &a1);
     CU_ASSERT_PTR_EQUAL(a1.parent, &a);
-    CU_ASSERT_TRUE(root.children_begin ? root.children_begin->children_begin == &a1 : 0);
+    CU_ASSERT_PTR_NOT_NULL(root.children_begin)
+    CU_ASSERT_PTR_EQUAL(root.children_begin->children_begin, &a1)
 }
 
 int main() {