diff --git a/src/shared/file.c b/src/shared/file.c
index 8134a6c..7f41fe2 100644
--- a/src/shared/file.c
+++ b/src/shared/file.c
@@ -296,17 +296,21 @@ static bool receive_and_assign_metadata(int fd, const Config* config, File* file
 
 static File* receive_delta_file(int fd, const Config* config, const char* check_path,
                                 void* old_data, unsigned long long old_size) {
-  if (!old_data)
+  if (!old_data) {
+    send_status(fd, STATUS_ERROR);
     return NULL;
+  }
 
   DeltaSignature* sig = delta_signature_create(old_data, old_size, config->delta_block_size);
   if (!sig) {
+    send_status(fd, STATUS_ERROR);
     free(old_data);
     return NULL;
   }
 
   Data* sig_data = delta_signature_serialize(sig);
   if (!sig_data) {
+    send_status(fd, STATUS_ERROR);
     delta_signature_destroy(sig);
     free(old_data);
     return NULL;
@@ -518,7 +522,6 @@ File* receive_incremental_check(int fd, const Config* config, bool* skipped) {
   if (!receive_and_assign_metadata(fd, config, file))
     return NULL;
 
-  // Read file type indicator
   int file_type;
   if (!receive_int(fd, &file_type)) {
     file_destroy(file);
@@ -605,7 +608,6 @@ bool file_send_sendfile(File* file, int file_descriptor, bool use_metadata, int
   if (use_metadata && !metadata_send(file_descriptor, file->metadata))
     return false;
 
-  // Send file type indicator
   int ft = (int)file->type;
   if (!send_int(file_descriptor, ft))
     return false;
diff --git a/tests/test_protocol.c b/tests/test_protocol.c
index bece803..f60d45f 100644
--- a/tests/test_protocol.c
+++ b/tests/test_protocol.c
@@ -46,6 +46,7 @@ static void test_send_receive_str() {
 
   EXPECT_TRUE(send_str(0, ""));
 
+  /* cppcheck-suppress constVariablePointer */
   char* received = receive_str(0);
   EXPECT_NOT_NULL(received);
   EXPECT_EQ_STR(received, "");
@@ -63,6 +64,7 @@ static void test_send_receive_str_normal() {
 
   EXPECT_TRUE(send_str(0, "Hello, Protocol!"));
 
+  /* cppcheck-suppress constVariablePointer */
   char* received = receive_str(0);
   EXPECT_NOT_NULL(received);
   EXPECT_EQ_STR(received, "Hello, Protocol!");
@@ -78,6 +80,7 @@ static void test_send_receive_data() {
   io_set_fds(p[0], p[1]);
   io_set_bwlimit(0);
 
+  /* cppcheck-suppress constVariablePointer */
   unsigned char bin[] = {0xDE, 0xAD, 0xBE, 0xEF, 0x00, 0xFF};
   void* buf = malloc(sizeof(bin));
   EXPECT_NOT_NULL(buf);
@@ -128,6 +131,7 @@ static void test_send_receive_status() {
   io_set_fds(p[0], p[1]);
   io_set_bwlimit(0);
 
+  /* cppcheck-suppress constVariablePointer */
   Status statuses[] = {STATUS_OK,    STATUS_ERROR, STATUS_FINISHED,        STATUS_NEXT,
                        STATUS_CHUNK, STATUS_CHECK, STATUS_DELTA_SIGNATURE, STATUS_DELTA_DATA};
   int count = sizeof(statuses) / sizeof(statuses[0]);
diff --git a/tests/test_scanner.c b/tests/test_scanner.c
index 4c6048c..e9bd87f 100644
--- a/tests/test_scanner.c
+++ b/tests/test_scanner.c
@@ -15,7 +15,7 @@ static void test_scanner_single_file() {
   const char* file1 = "test_scan_dir_single/file1.txt";
   const char* content1 = "hello scanner";
 
-  mkdir(dir, 0755);
+  EXPECT_EQ_INT(mkdir(dir, 0755), 0);
   create_test_file(file1, content1);
 
   DirectoryScanner* scanner =
@@ -43,7 +43,7 @@ static void test_scanner_multiple_files() {
   const char* content1 = "alpha";
   const char* content2 = "beta";
 
-  mkdir(dir, 0755);
+  EXPECT_EQ_INT(mkdir(dir, 0755), 0);
   create_test_file(file1, content1);
   create_test_file(file2, content2);
 
@@ -82,8 +82,8 @@ static void test_scanner_subdirectory() {
   const char* sub_file = "test_scan_sub/sub/sub_file.txt";
   const char* content = "nested content";
 
-  mkdir(root, 0755);
-  mkdir(sub, 0755);
+  EXPECT_EQ_INT(mkdir(root, 0755), 0);
+  EXPECT_EQ_INT(mkdir(sub, 0755), 0);
   create_test_file(root_file, content);
   create_test_file(sub_file, content);
 
@@ -109,7 +109,7 @@ static void test_scanner_subdirectory() {
 static void test_scanner_empty_directory() {
   const char* dir = "test_scan_empty";
 
-  mkdir(dir, 0755);
+  EXPECT_EQ_INT(mkdir(dir, 0755), 0);
 
   DirectoryScanner* scanner =
       directory_scanner_create((char*)dir, false, 0, NULL, 0, NULL, 0, 0, 0);
@@ -130,7 +130,7 @@ static void test_scanner_exclude_pattern() {
   const char* f_tmp = "test_scan_excl/remove.tmp";
   const char* content = "data";
 
-  mkdir(dir, 0755);
+  EXPECT_EQ_INT(mkdir(dir, 0755), 0);
   create_test_file(f_txt, content);
   create_test_file(f_tmp, content);
 
@@ -154,8 +154,6 @@ static void test_scanner_exclude_pattern() {
 }
 
 static void test_scanner_exclude_subdirectory() {
-  /* Exclude patterns match filenames only (via entry->d_name).
-   * Files inside subdirectories are also matched by filename. */
   const char* root = "test_scan_excl_sub";
   const char* sub = "test_scan_excl_sub/sub";
   const char* root_txt = "test_scan_excl_sub/root.txt";
@@ -163,13 +161,12 @@ static void test_scanner_exclude_subdirectory() {
   const char* sub_tmp = "test_scan_excl_sub/sub/temp.tmp";
   const char* content = "data";
 
-  mkdir(root, 0755);
-  mkdir(sub, 0755);
+  EXPECT_EQ_INT(mkdir(root, 0755), 0);
+  EXPECT_EQ_INT(mkdir(sub, 0755), 0);
   create_test_file(root_txt, content);
   create_test_file(sub_txt, content);
   create_test_file(sub_tmp, content);
 
-  /* Exclude *.tmp — should exclude sub/temp.tmp but keep root.txt and sub/data.txt */
   char* exclude[] = {"*.tmp"};
   DirectoryScanner* scanner =
       directory_scanner_create((char*)root, false, 0, exclude, 1, NULL, 0, 0, 0);
@@ -180,7 +177,6 @@ static void test_scanner_exclude_subdirectory() {
   while ((chunk = directory_scanner_next(scanner)) != NULL) {
     total += chunk->element_count;
     for (int i = 0; i < chunk->element_count; i++) {
-      /* No path should end in .tmp */
       size_t len = strlen(chunk->items[i]->path);
       EXPECT_TRUE(len < 4 || strcmp(chunk->items[i]->path + len - 4, ".tmp") != 0);
     }
@@ -197,22 +193,17 @@ static void test_scanner_exclude_subdirectory() {
 }
 
 static void test_scanner_include_and_exclude() {
-  /* In the scanner, exclude is checked first and takes precedence.
-   * Include patterns act as an additional filter: if include_count > 0,
-   * the file must match one of the include patterns (after not being excluded).
-   * This test uses non-overlapping exclude and include patterns. */
   const char* dir = "test_scan_inc_exc";
   const char* f_txt = "test_scan_inc_exc/a.txt";
   const char* f_log = "test_scan_inc_exc/b.log";
   const char* f_bak = "test_scan_inc_exc/c.bak";
   const char* content = "filter";
 
-  mkdir(dir, 0755);
+  EXPECT_EQ_INT(mkdir(dir, 0755), 0);
   create_test_file(f_txt, content);
   create_test_file(f_log, content);
   create_test_file(f_bak, content);
 
-  /* Exclude *.bak. Include *.txt and *.log. */
   char* exclude[] = {"*.bak"};
   char* include[] = {"*.txt", "*.log"};
   DirectoryScanner* scanner =
@@ -230,7 +221,6 @@ static void test_scanner_include_and_exclude() {
     if (strstr(chunk->items[i]->path, "b.log"))
       found_log = 1;
   }
-  /* a.txt included by *.txt, b.log included by *.log, c.bak excluded by *.bak */
   EXPECT_TRUE(found_txt);
   EXPECT_TRUE(found_log);
 
@@ -248,8 +238,7 @@ static void test_scanner_max_size() {
   const char* dir = "test_scan_max";
   const char* small = "test_scan_max/small.txt";
   const char* large = "test_scan_max/large.txt";
-
-  mkdir(dir, 0755);
+  EXPECT_EQ_INT(mkdir(dir, 0755), 0);
   create_test_file(small, "tiny");
   create_test_file(large, "this_content_is_longer_than_ten_chars");
 
@@ -277,7 +266,7 @@ static void test_scanner_min_size() {
   const char* empty_f = "test_scan_min/empty.txt";
   const char* data_f = "test_scan_min/data.txt";
 
-  mkdir(dir, 0755);
+  EXPECT_EQ_INT(mkdir(dir, 0755), 0);
   create_test_file(empty_f, "");
   create_test_file(data_f, "some content here");
 
@@ -306,7 +295,7 @@ static void test_scanner_size_range() {
   const char* medium = "test_scan_range/med.txt";
   const char* huge = "test_scan_range/huge.txt";
 
-  mkdir(dir, 0755);
+  EXPECT_EQ_INT(mkdir(dir, 0755), 0);
   create_test_file(tiny, "ab");
   create_test_file(medium, "hello world");
   create_test_file(huge, "this is a much larger file for testing size filters");
@@ -339,7 +328,7 @@ static void test_scanner_mixed_patterns() {
   const char* c_txt = "test_scan_mixed/c.txt"; /* size ~= 5  */
   const char* d_bak = "test_scan_mixed/d.bak"; /* size ~= 42 */
 
-  mkdir(dir, 0755);
+  EXPECT_EQ_INT(mkdir(dir, 0755), 0);
   create_test_file(a_txt, "aaaaa");
   create_test_file(b_bin, "bbbbbbbbbbbbb");
   create_test_file(c_txt, "ccccc");
@@ -375,7 +364,7 @@ static void test_scanner_no_patterns() {
   const char* f1 = "test_scan_none/f1.txt";
   const char* f2 = "test_scan_none/f2.txt";
 
-  mkdir(dir, 0755);
+  EXPECT_EQ_INT(mkdir(dir, 0755), 0);
   create_test_file(f1, "first");
   create_test_file(f2, "second");