test that connections are closed on gc

qcodes/tests/test_visa.py

@@ -1,3 +1,5 @@
+import gc
+import logging
 import re
 from pathlib import Path
 
@@ -6,7 +8,8 @@
 import pyvisa.constants
 from pytest import FixtureRequest
 
-from qcodes.instrument.visa import VisaInstrument
+from qcodes.instrument import Instrument, VisaInstrument
+from qcodes.instrument_drivers.american_magnetics import AMIModel430
 from qcodes.validators import Numbers
 
 
@@ -109,6 +112,33 @@ def _make_mock_visa():
         mv.close()
 
 
+def test_visa_gc_closes_connection(caplog) -> None:
+    def use_magnet():
+        _ = AMIModel430(
+            "x",
+            address="GPIB::1::INSTR",
+            pyvisa_sim_file="AMI430.yaml",
+            terminator="\n",
+        )
+        assert list(Instrument._all_instruments.keys()) == ["x"]
+
+    # ensure that any unused instruments that have not been gced are gced before running
+    gc.collect()
+    caplog.clear()
+    with caplog.at_level(logging.INFO, logger="qcodes.instrument.visa"):
+        use_magnet()
+        gc.collect()
+    # at this stage the instrument created in use_magnet has gone out of scope
+    # and we have triggered an explicit gc so the finalize method has been triggered/
+    # We test this
+    # and the instrument should no longer be in the instrument registry
+    assert list(Instrument._all_instruments.keys()) == []
+    assert (
+        caplog.records[-1].message
+        == "Closing VISA handle to x as there are no non weak references to the instrument."
+    )
+
+
 def test_ask_write_local(mock_visa) -> None:
 
     # test normal ask and write behavior