test_trinity_cli: Add Trinity attach web3 interaction test.

The test attaches to running Trinity and interacts with the console.
Verifies that the w3 object is available and is able to read network
version.

Bases on Christoph Burgdorf's [[email protected]] test skeleton.

Fixes: ethereum#1472

Author: cryptomental

setup.py

@@ -52,6 +52,7 @@
     ],
     'test': [
         "hypothesis==3.69.5",
+        "pexpect>=4.6, <5",
         # pinned to <3.7 until async fixtures work again
         # https://github.com/pytest-dev/pytest-asyncio/issues/89
         "pytest>=3.6,<3.7",

tests/trinity/integration/test_trinity_cli.py

@@ -1,3 +1,5 @@
+import sys
+import pexpect
 import pytest
 
 from trinity.tools.async_process_runner import AsyncProcessRunner
@@ -109,6 +111,34 @@ async def test_light_boot(async_process_runner, command):
     })
 
 
+@pytest.mark.parametrize(
+    'command',
+    (
+        ('trinity', ),
+    )
+)
+@pytest.mark.asyncio
+async def test_web3(command, async_process_runner):
+    await async_process_runner.run(command, timeout_sec=30)
+    assert await contains_all(async_process_runner.stderr, {
+        "Started DB server process",
+        "Started networking process",
+        "IPC started at",
+    })
+
+    attached_trinity = pexpect.spawn('trinity', ['attach'], logfile=sys.stdout)
+    try:
+        attached_trinity.expect("An instance of Web3 connected to the running chain")
+        attached_trinity.sendline("w3.net.version")
+        attached_trinity.expect("'1'")
+        attached_trinity.sendline("w3")
+        attached_trinity.expect("web3.main.Web3")
+    except pexpect.TIMEOUT:
+        raise Exception("Trinity attach timeout")
+    finally:
+        attached_trinity.close()
+
+
 @pytest.mark.parametrize(
     'command',
     (