Add smoke test for frontend commands

This ensures that at least --help works for all the commands,
preventing regressions like that in f3323a35d5.

artiq/test/test_frontends.py

@@ -0,0 +1,35 @@
+"""Generic tests for frontend commands."""
+import subprocess
+import sys
+import unittest
+
+
+class TestFrontends(unittest.TestCase):
+    def test_help(self):
+        """Test --help as a simple smoke test against catastrophic breakage."""
+        commands = {
+            "aqctl": [
+                "corelog", "korad_ka3005p", "lda", "novatech409b",
+                "thorlabs_tcube"
+            ],
+            "artiq": [
+                "client", "compile", "coreanalyzer", "coremgmt", "ctlmgr",
+                "devtool", "flash", "influxdb", "master", "mkfs", "route",
+                "rpctool", "rtiomon", "run", "session"
+            ]
+        }
+
+        # Skip tests for GUI programs on headless CI environments.
+        try:
+            from PyQt5 import QtGui, QtWidgets
+            commands["artiq"] += ["browser", "dashboard"]
+        except ImportError:
+            pass
+
+        for module in (prefix + "_" + name
+                       for prefix, names in commands.items()
+                       for name in names):
+            subprocess.check_call(
+                [sys.executable, "-m", "artiq.frontend." + module, "--help"],
+                stdout=subprocess.DEVNULL,
+                stderr=subprocess.STDOUT)