tests: start the journalctl tail before it is needed

iter_output() waited until its caller's first next() call to spawn
the journalctl tail, which could lead to log traffic being missed,
hanging next() forever: start the tail right away instead.

cmdeploy/src/cmdeploy/tests/online/test_1_basic.py

@@ -13,7 +13,8 @@ from cmdeploy.cmdeploy import get_sshexec
 
 class TestSSHExecutor:
     @pytest.fixture(scope="class")
-    def sshexec(self, sshdomain):
+    @classmethod
+    def sshexec(cls, sshdomain):
         return get_sshexec(sshdomain)
 
     def test_ls(self, sshexec):

cmdeploy/src/cmdeploy/tests/plugin.py

@@ -411,6 +411,7 @@ class Remote:
         self._procs = []
 
     def iter_output(self, logcmd="", ready=None):
+        # run popen run here so the tail is live before caller triggers
         getjournal = "journalctl -f" if not logcmd else logcmd
         print(self.sshdomain)
         if self.sshdomain in ("@local", "localhost"):
@@ -425,6 +426,10 @@ class Remote:
             stderr=subprocess.DEVNULL,
         )
         self._procs.append(popen)
+        return self._read_lines(popen, ready)
+
+    @staticmethod
+    def _read_lines(popen, ready):
         try:
             while 1:
                 line = popen.stdout.readline()

cmdeploy/src/cmdeploy/tests/test_remote_iter_output.py

@@ -0,0 +1,34 @@
+from cmdeploy.tests.plugin import Remote
+
+
+def _script(tmp_path, name, body):
+    # iter_output splits its command string on whitespace, so any command
+    # with embedded spaces has to live in a file, not an inline string.
+    path = tmp_path / name
+    path.write_text(f"#!/bin/sh\n{body}\n")
+    path.chmod(0o755)
+    return str(path)
+
+
+def test_iter_output_spawns_before_first_next(tmp_path):
+    """The tail process must be live before the caller triggers or fast-moving logs can be missed"""
+    script = _script(tmp_path, "late.sh", "sleep 0.2\necho late-line")
+    remote = Remote("@local")
+    lineproducer = remote.iter_output(script)
+    assert remote._procs, "Popen must run on iter_output() itself, not on first next()"
+    assert remote._procs[0].poll() is None
+    assert next(lineproducer) == "late-line"
+    remote.close()
+
+
+def test_iter_output_ready_fires_after_first_line(tmp_path):
+    """ready() must wait for the first real line, not fire at spawn time"""
+    script = _script(tmp_path, "trigger.sh", "echo backlog\nsleep 0.2\necho trigger-fired")
+    remote = Remote("@local")
+    calls = []
+    lineproducer = remote.iter_output(script, ready=lambda: calls.append(1))
+    assert calls == []
+    assert next(lineproducer) == "backlog"
+    assert calls == [1]
+    assert next(lineproducer) == "trigger-fired"
+    remote.close()