Merge bitcoin/bitcoin#27852: test: add coverage to rpc_blockchain.py

376dc2c test: add coverage to rpc_blockchain.py (kevkevin)

Pull request description:

  Included a test that checks the functionality of setting
  the first param of getnetworkhashps to negative value returns
  the average network hashes per second from the last difficulty change.

ACKs for top commit:
  jlopp:
    tACK bitcoin/bitcoin@376dc2c
  achow101:
    ACK 376dc2c
  ismaelsadeeq:
    Tested ACK 376dc2c
  pablomartin4btc:
    tACK 376dc2c

Tree-SHA512: 02d52f622e9cb7a1240c5d124510dd75d03f696f119b2625b0befd60b004ec50ff1a2d5515e0e227601adeecd837e0778ed131ee2a8c5f75f1b824be711213a7

Author: achow101

test/functional/rpc_blockchain.py

@@ -58,6 +58,7 @@
 TIME_RANGE_MTP = TIME_GENESIS_BLOCK + (HEIGHT - 6) * TIME_RANGE_STEP
 TIME_RANGE_TIP = TIME_GENESIS_BLOCK + (HEIGHT - 1) * TIME_RANGE_STEP
 TIME_RANGE_END = TIME_GENESIS_BLOCK + HEIGHT * TIME_RANGE_STEP
+DIFFICULTY_ADJUSTMENT_INTERVAL = 2016
 
 
 class BlockchainTest(BitcoinTestFramework):
@@ -451,6 +452,15 @@ def _test_getnetworkhashps(self):
         # This should be 2 hashes every 10 minutes or 1/300
         assert abs(hashes_per_second * 300 - 1) < 0.0001
 
+        # Test setting the first param of getnetworkhashps to negative value returns the average network
+        # hashes per second from the last difficulty change.
+        current_block_height = self.nodes[0].getmininginfo()['blocks']
+        blocks_since_last_diff_change = current_block_height % DIFFICULTY_ADJUSTMENT_INTERVAL + 1
+        expected_hashes_per_second_since_diff_change = self.nodes[0].getnetworkhashps(blocks_since_last_diff_change)
+
+        assert_equal(self.nodes[0].getnetworkhashps(-1), expected_hashes_per_second_since_diff_change)
+        assert_equal(self.nodes[0].getnetworkhashps(-2), expected_hashes_per_second_since_diff_change)
+
     def _test_stopatheight(self):
         self.log.info("Test stopping at height")
         assert_equal(self.nodes[0].getblockcount(), HEIGHT)