Prover tests for empty / nonempty blocks

[OlivierBBB]

@bogdanbear requested we provide tests with

• a mixture of empty and nonempty blocks
  • we already have such tests, but we need to cover the following variants:
    • first block is empty: yes / no
    • last block is empty: yes / no
• a conflation of all empty blocks
  • one block variant
  • multi block variant