Test: insert and merge metadata

tests/test_metadata_stream.liq

@@ -30,11 +30,32 @@ def on_metadata_notification(metadata) =
 end
 
 # Save the callback
+last_metadata = in_stream.last_metadata
 imcb = in_stream.insert_metadata
 
+# Ability to insert and merge with previous metadata
+def insert_merged_meta(meta) =
+    lm = (last_metadata() ?? [])
+    merged = ref(lm)
+
+    def add_meta_entry(entry) =
+        print("Add entry #{entry}")
+        let (k, v) = entry
+        if list.assoc.mem(k, !merged) then
+            print("Remove existing entry #{entry} with key #{k}")
+            merged := list.assoc.remove(k, !merged)
+        end
+        merged := list.add(entry, !merged)
+    end
+
+    list.iter(add_meta_entry, (meta))
+    print("MERGED META: #{!merged}")
+    imcb(!merged)
+end
+
 in_stream = source.on_metadata(id="in_stream", in_stream, on_metadata_notification)
 output.alsa(id="lineout", device="default", mksafe(in_stream))
 
 # Later:
 meta = [("foo", "bar")]
-thread.run(every=3., { imcb(meta) })
+thread.run(every=3., { insert_merged_meta(meta) })