John 16:4 says Jesus told them so they remember when it happens — directly parallels the forewarning that leads to testimony.

1 Thessalonians 3:4 confirms that persecution was foretold and occurred — the context for the testimony promised here.

Philippians 1:28 shows a fearless response to opposition becomes a testimony — parallel to the testimony promised here.

2 Thessalonians 1:5 connects suffering for the kingdom to being counted worthy — parallel to the testimony that results from persecution here.