Make flaky test not flaky

Author: FelonEkonom

test/membrane_http_adaptive_stream/integration_test/source_test.exs

@@ -192,9 +192,7 @@ defmodule Membrane.HTTPAdaptiveStream.Source.Test do
     test "Live HLS stream played from the middle", %{tmp_dir: tmp_dir} do
       index_m3u8 = Path.join(tmp_dir, "index.m3u8")
       generate_live_hls(@bbb_33s_mp4_url, index_m3u8)
-
-      await_until_file_exists(index_m3u8)
-      Process.sleep(20_000)
+      :ok = await_until_media_sequence_is_3(index_m3u8)
 
       spec =
         child(:hls_source, %Membrane.HTTPAdaptiveStream.Source{
@@ -253,6 +251,18 @@ defmodule Membrane.HTTPAdaptiveStream.Source.Test do
     end
   end
 
+  defp await_until_media_sequence_is_3(index_m3u8) do
+    with {:ok, content} <- File.read(index_m3u8),
+         true <- String.contains?(content, "#EXT-X-MEDIA-SEQUENCE:3") do
+      :ok
+    else
+      _error ->
+        Logger.debug("Waiting for media sequence to be 3...")
+        Process.sleep(100)
+        await_until_media_sequence_is_3(index_m3u8)
+    end
+  end
+
   defp generate_live_hls(source_mp4, index_m3u8) do
     start_supervised!(
       {