bitcoind: Fix blockHash ZMQ test #2745
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We send a `stop` RPC call and wait for the subprocess after receiving a `success/ok` message. This is unnecessary because we received a `success` reply already.
We parse stdout and wait for the "init message: Done loading" line to detect when bitcoind is ready. After seeing this line, we stop reading stdout causing the stdout buffer to fill up. When the stdout buffer fills up, bitcoind waits until its parent process reads from it but this unfortunately never happens leading to a deadlock.
The assumptions and expectations of the tests are wrong.
The test mines blocks and waits until it sees the block hashes of the mined blocks over ZMQ. Unfortunately, ZMQ publishers are stateless and can't re-transmit lost messages [1]. Consequently, the test was wrong. The fixed test subscribes to the publisher, starts mining blocks, and waits until it observes a new block hash. [1] https://zguide.zeromq.org/docs/chapter5/#Pros-and-Cons-of-Pub-Sub
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The test mines blocks and waits until it sees the block hashes of the
mined blocks over ZMQ. Unfortunately, ZMQ publishers are stateless and
can't re-transmit lost messages [1]. Consequently, the test was wrong.
The fixed test subscribes to the publisher, starts mining blocks, and
waits until it observes a new block hash.