Added a test for basic counting accuracy

config/schema/archive_tree.schema.yml

@@ -0,0 +1,12 @@
+block.settings.archive_tree:
+  type: block_settings
+  label: 'Archive Tree block settings'
+  mapping:
+    content_types:
+      type: sequence
+      label: 'Content types'
+      sequence:
+        type: string
+    expand_years:
+      type: boolean
+      label: 'Expand years by default'