spiffs: add test case for readdir_r with large number of files

Ref. https://esp32.com/viewtopic.php?f=13&t=6486

components/spiffs/test/test_spiffs.c

@@ -275,6 +275,63 @@ void test_spiffs_opendir_readdir_rewinddir(const char* dir_prefix)
     TEST_ASSERT_EQUAL(0, closedir(dir));
 }
 
+void test_spiffs_readdir_many_files(const char* dir_prefix)
+{
+    const int n_files = 40;
+    const int n_folders = 4;
+    unsigned char file_count[n_files * n_folders];
+    memset(file_count, 0, sizeof(file_count)/sizeof(file_count[0]));
+    char file_name[ESP_VFS_PATH_MAX + CONFIG_SPIFFS_OBJ_NAME_LEN];
+
+    /* clean stale files before the test */
+    DIR* dir = opendir(dir_prefix);
+    if (dir) {
+        while (true) {
+            struct dirent* de = readdir(dir);
+            if (!de) {
+                break;
+            }
+            snprintf(file_name, sizeof(file_name), "%s/%s", dir_prefix, de->d_name);
+            unlink(file_name);
+        }
+    }
+
+    /* create files */
+    for (int d = 0; d < n_folders; ++d) {
+        printf("filling directory %d\n", d);
+        for (int f = 0; f < n_files; ++f) {
+            snprintf(file_name, sizeof(file_name), "%s/%d/%d.txt", dir_prefix, d, f);
+            test_spiffs_create_file_with_text(file_name, file_name);
+        }
+    }
+
+    /* list files */
+    for (int d = 0; d < n_folders; ++d) {
+        printf("listing files in directory %d\n", d);
+        snprintf(file_name, sizeof(file_name), "%s/%d", dir_prefix, d);
+        dir = opendir(file_name);
+        TEST_ASSERT_NOT_NULL(dir);
+        while (true) {
+            struct dirent* de = readdir(dir);
+            if (!de) {
+                break;
+            }
+            int file_id;
+            TEST_ASSERT_EQUAL(1, sscanf(de->d_name, "%d.txt", &file_id));
+            file_count[file_id + d * n_files]++;
+        }
+        closedir(dir);
+    }
+
+    /* check that all created files have been seen */
+    for (int d = 0; d < n_folders; ++d) {
+        printf("checking that all files have been found in directory %d\n", d);
+        for (int f = 0; f < n_files; ++f) {
+            TEST_ASSERT_EQUAL(1, file_count[f + d * n_files]);
+        }
+    }
+}
+
 
 typedef struct {
     const char* filename;
@@ -537,6 +594,13 @@ TEST_CASE("opendir, readdir, rewinddir, seekdir work as expected", "[spiffs]")
     test_teardown();
 }
 
+TEST_CASE("readdir with large number of files", "[spiffs][timeout=15]")
+{
+    test_setup();
+    test_spiffs_readdir_many_files("/spiffs/dir2");
+    test_teardown();
+}
+
 TEST_CASE("multiple tasks can use same volume", "[spiffs]")
 {
     test_setup();