A test double that "looks like a port" to ProtonStream.

Instead of spawning the muontrap executable, ProtonStream can be configured with fake: test_pid. When faked, every port operation is forwarded to test_pid as a message, and the ProtonStream GenServer itself stands in for the port handle. This lets a test drive and observe the process I/O entirely with assert_receive/refute_receive.

Message vocabulary

Messages sent to the test pid by the fake:

• {:protonstream_open, command, ps} - the fake "port" was opened for command. ps is the ProtonStream GenServer pid and is the handle you use to inject artificial output.
• {:protonstream_command, ps, frame} - ProtonStream wrote frame (a framed stdin/ack binary) to the port.
• {:protonstream_closed, ps} - the port was closed.

To inject port output, the test calls send_data/2, which sends the ProtonStream GenServer a {test_pid, {:data, frames}} message - the same shape a real port uses. frames must speak the framed wire protocol (see stdout_frame/1, stderr_frame/1, and exit_frame/1).

Example

{:ok, ps} = ProtonStream.open("cat", [], fake: self())
^ps = ProtonStream.Fake.assert_opened("cat")

# observe what ProtonStream writes to stdin
send(ps, {self(), {:command, "hello"}})
assert_receive {:protonstream_command, ^ps, <<1, 0, 5, "hello">>}

# inject artificial stdout back to the owner
ProtonStream.Fake.send_data(ps, ProtonStream.Fake.stdout_frame("hi\n"))
assert_receive {^ps, {:data, "hi\n"}}

ProtonStream.Fake.send_data(ps, ProtonStream.Fake.exit_frame(0))